A comprehensive approach to an urban water reuse system to meet irrigation demand and conserve water: City of Cape Coral, FL, USA

The City of Cape Coral was first developed from raw land in the 1950s by the Rosen Brothers and was incorporated as a city in 1970. It is currently one of the fastest growing communities in the United States with a counted population of 196,290 in 2020 and a current estimated population of 221,997, a growth of over 13% in only 3 years (United States Census Bureau 2024). Beginning in 1991, the City of Cape Coral began installing large diameter reuse water mains and utilized smaller diameter potable water mains to serve large residential and commercial properties. Since impact and connection fees are significantly lower to connect to the reclaimed water system for continuously pressurized fire sprinklers and fire hydrants, many property owners viewed the system positively. Since 1991, the City of Cape Coral has significantly expanded the irrigation network (IRN) by constructing six freshwater canal pump stations and expanded the water reclamation facility storage, irrigation distribution network, and pumping capacity. Now that the irrigation system has matured over the past 30 years and has over 60,000 irrigation connections, additional demands are causing reliability issues with pressures, flow, and increased energy consumption. This issue is occurring more commonly during the dry season, which typically begins in October and ends in May.

Because drought in anthropogenic systems is driven by an imbalance between water use and available supply, urban drought risk is influenced in part by the dynamics of each water demand, both over the long term and specifically during periods of water shortage (Bragalli et al. 2007; Padowski & Jawitz 2012; Van Loon et al. 2016). Pressurized IRNs help improve the efficiency of water resources use compared with other distribution systems, such as open channels (Fernandez Garcıa et al. 2014). However, in pressurized systems, energy consumption is relatively high owing to the need for pumping stations to maintain the required pressure (Fernandez Garcıa et al. 2013). This fact, along with increasing energy costs, makes it necessary to develop tools to optimize the efficiency of this type of infrastructure (Corcoles et al. 2016).

When designing pumping stations, only high discharges are typically considered to determine the design flow, but in most cases, low and medium discharges are generated (Moreno et al. 2010). This can cause pumping stations to operate at lower efficiency (Perez Urrestarazu et al. 2012). This fact is important with on-demand IRNs and is related to the high variability of discharges and the required pumping head changes that occur during the peak irrigation season (Lamaddalena & Sagardoy 2000). Commonly, managers of IRNs regulate the pumping stations with the lowest pressure possible that still enables the system to work in an adequate manner (Corcoles et al. 2016). However, this required pressure could be insufficient for low or medium discharges and make the pumps work at an inappropriate operating load, decreasing energy efficiency (Corcoles et al. 2016). In most of the studies where the performance of pumping systems is analyzed, a high constant efficiency independent of the discharge is assumed, but this parameter can vary for each pumping station depending on the discharges from the segment of the system and pumping heads used (Corcoles et al. 2016).

In southwest Florida, the dry and wet seasons have been extremely unpredictable over the past 20 years (South Florida Water Management District 2022, 2023a, b). Among the myriad of threats that are expected to intensify under the effects of climate change is an increased risk of urban water supply shortages, wherein water supplies and/or infrastructure are temporarily incapable of meeting the water demand (Cromwell et al. 2007; Ginley & Ralston 2010; Bloetcher et al. 2011; Buurman et al. 2017; Maliva et al. 2021). The city uses a 483-km freshwater canal system as a reservoir to supplement the reclaimed water. However, since 2001, the dry season rainfall in southwest Florida has not been sufficient to keep the reservoir hydrated.

Unfortunately, water scarcity and rainfall fluctuation are increasing in many parts of the world due to climate change, population, and economic growth (Distefano & Kelly 2017). Mitigation of the impacts of climate change on water resource requires mixed portfolios of supply and demand adaptation measures. So far, the debate on adaptation at the local level has mainly focused on the definition of efficient, robust, and flexible adaptation portfolios as measures to adjust system management to mitigate uncertainty associated with future climate and demand scenarios (Hallegatte 2009; Lempert & Groves 2010; Walker et al. 2013; Girard et al. 2015; Kwakkel et al. 2015). Current and future water supplies and demands are also highly uncertain due to poorly defined climate change impacts and population projections in high growth regions (Milly et al. 2008). Therefore, water managers need to both increase the water supply options and control the increase in demand.

The City of Cape Coral has approximately 840 reclaimed water fire hydrants that require the system to be continuously pressurized. During the early stages of reclaimed water adoption, many people and water managers thought it was a great idea to connect fire hydrants to the reclaimed water system for system maintenance and fire protection. However, future management methods for natural resource systems will likely differ due to changes in policy, governance, and legal frameworks that address extreme changes in water supplies. Beginning in 2005, the city ceased the practice of allowing private businesses to connect to the reclaimed water system for fire sprinkler systems. In 2014, the city passed an ordinance prohibiting reclaimed water fire hydrants from being used to satisfy fire protection for all new multifamily and commercial structures based on fluctuations of pressure within the reuse system (requires Class 1 reliability).

As part of the planning process, it was necessary to evaluate future water use and ascertain how to meet the demand. Water use restrictions, which impose limits on the timing and frequency with which water can be used outdoors and/or specifically for irrigating lawns and gardens, are key features of drought mitigation plans implemented by cities across the globe (Kenney et al. 2004; Carrière et al. 2006; Chong & White 2007; Knutson 2008; Golembesky et al. 2009; Buurman et al. 2017). Although temporary drought restrictions have been common practice since the 1970s, the imposition of permanent water use restrictions has become more widespread over the past few decades as aging municipal water systems struggle to keep pace with growing cities and an increasingly variable climate (Hilaire et al. 2008; Shandas et al. 2015; Milman & Polsky 2016). Historically, year-round watering restrictions, which are required in the State of Florida, have not proven beneficial for public and privately operated utilities. Temporary drought restrictions have generally proven to be effective tools for restraining municipal water demands during periods of drought, reducing overall water production by as much as 56% in some cases (Kenney et al. 2004; Mayer et al. 2015). These restrictions tend to be most effective when they are stringent, mandatory, and enforced (Shaw et al. 1992; Kenney et al. 2004). However, permanent restrictions applied irrespective of drought conditions may not produce the same impact (Finley & Basu 2020). Multiple studies have found that policies enacted to curb excess water use are most effective when users themselves perceive the need for such actions (Bruvold 1979; Gilbertson et al. 2011; Quesnel & Ajami 2017; Hannibal et al. 2018). For this reason, permanent water use restrictions that are enforced regardless of climate conditions may not inspire the same degree of water savings as drought restrictions accompanied by climate signals and/or evidence of physical water shortage that directly impact users and the environment (Kenney et al. 2004). For example, when a water user can no longer use a boat, because the canal behind a house is dry, there tends to be public concern and cooperation.

Unfortunately, little research exists to confirm or quantify the effects of permanent restrictions on outdoor water use (Survis & Root 2012; Castledine et al. 2014). Some water efficiency professionals have even speculated informally that less-stringent water restrictions such as odd–even day watering limits may in fact lead to increased outdoor water use (Ontario Water Works Association 2008). Year-round watering restrictions in Cape Coral use the last number of the property address to determine the watering schedule. Use of an even–odd or last number of property address irrigation schedule has not proven beneficial since they did not take into consideration the impacts to the daily operations of water distribution systems. Year-round watering schedules were more concerned with achieving water conservation by limiting watering to 2 or 3 days/week than the consequences that irrigation water demands would have on the operation of the potable or non-potable water infrastructure. Typically, potable water systems are designed for a high level of reliability with respect to source water, flows, and pressure (Class I reliability). Nationwide, most potable water treatment facilities rely on extensive and diversified surface water and ground water sources. However, the same cannot be assumed for separate reclaimed/dual non-potable water systems. Reclaimed water systems typically rely on a variable supply of treated wastewater effluent or a combination of surface water storage originating from storm water storage and treated wastewater effluent. Therefore, reclaimed water systems are now becoming more vulnerable during extended dry periods. Surface water storage reservoirs can quickly deplete from use and evaporation. The objective of this research is to examine the past 5 years of daily water production records to allow (a) simulation of how the water demand will change using three unique scenarios, (b) evaluation of the effectiveness of the City of Cape Coral current watering restrictions on water pressures and energy consumption, and (c) development of possible solutions for improving the operational reliability and sustainability of the irrigation system by expanding watering schedules and regulations for new efficient irrigation systems that qualify for a variance from the watering schedule. This study analyzes part of the City of Cape Coral's ongoing water resource management planning, incorporating changes to the original assumptions based on operational data and forward-looking modeling. The parameters in our simulations reflect both the current practices and potential future projections. The Environmental Resource Assessment and Management System (eRAMS) Integrated Urban Water Management software is used to evaluate these scenarios and to develop alternative solutions that address irrigation water demand, enhance wastewater reuse, and reduce environmental discharges.

Catena Analytics produced a state-of-the art technology platform that provides custom tools for managing water with links to environmental resources (Catena Analytics 2021). The eRAMS Urban Planning and Management System software allows users to forecast urban water demand and project future potential savings and management of demand. The tool used in this analysis is specific to water demand forecasting based on customized inputs and unique local conditions. The eRAMS Integrated Urban Water Model (IUWM) is a high-level planning tool that allows urban planners and water managers to consider potable water savings of indoor and outdoor conservation measures and alternative water sources such as graywater, stormwater, and reclaimed water (Catena Analytics 2021).

In this study, the eRAMS IUWM software evaluates current practices and future scenarios to develop comprehensive solutions that effectively address irrigation water demand, enhance the reuse of wastewater, and reduce environmental discharges. Scenarios are based on predicted irrigation demands that exceed supply, with current irrigation water flows potentially augmented by various local water sources or water management options, as reported in the report by MWH (2011). In addition, changes to original assumptions are considered based on operational data. The study also analyzes future scenarios to assess proposed alternative solutions. This approach aims to support better decision-making for water resource management amid evolving environmental conditions and urban growth.

IRN data were obtained from the City of Cape Coral Utilities Department pressurized IRN daily operating reports and the annual Florida Department of Environmental Protection (FDEP) reuse reports. Pressure and pumping flow data were obtained from 1 October 2016 through 30 September 2021 (60 months). The data were based on historical daily pumping and pressure reports maintained by the city. The IRN data containing daily minimum and maximum pressures and total pumping rates in m³/day were plotted for each canal pumping station and pressure recorder located in the center, southeast, southwest, northeast, and northwest quadrants of the city.

The pumping and pressure data were grouped by the day of the week to determine which days of the week have the highest demands and impacts on water pressure in bar (converted from pounds per square inch). GIS data were obtained from the city to determine the number of homes and businesses ending with the addresses numbers 0–9, which are used to manage the irrigation use volume. Then, the exact number of homes were determined that are permitted to irrigate on a particular day of the week based on the current watering restrictions enacted by the city.

Lee County monthly rainfall data were obtained and tabulated on a spreadsheet for the period from 1992 to October 2021. From the Lee County, Florida, data, the wettest and driest months based on the mean rainfall in cm (inches) were determined. Since Tuesday was a no watering day in Cape Coral during this period, it was excluded from the analysis. The data were used as input into the eRAMS model simulation to assess the sensitivity of conservation measures on monthly water demands if high-efficiency sprinkler systems were to become more prevalent or mandatory in the city.

The eRAMS IUWM is utilized to assess various current and potential future water demand scenarios. eRAMS has sophisticated graphing capabilities that enable the user to evaluate the impact of land use configurations, changes in climate, conservation programs, and alternative water sources on water supply demands. The graphing tools can be tailored to the needs of the user and exported along with the raw data (Catena Analytics 2021). Three scenarios were developed and analyzed using eRAMS IUWM software, based on both present and future plans of the City of Cape Coral, including plausible future scenarios. The scenarios incorporate key water use and management options. For instance, Scenario 1 assessed irrigation water use sensitivity with an estimated efficiency rate of 35% for 2021. In Scenario 2, irrigation system efficiency improved by 15%, while Scenario 3 targeted a 21% increase from the efficiency level established in Scenario 2.

Scenario 1 serves as the baseline, emphasizing the inefficiency of many automatic sprinkler systems in the city, leading to water wastage. Future efforts include enforcing a conservation ordinance, requiring new irrigation systems to adhere to higher efficiency standards. These scenarios aim to evaluate the potential effects of improved irrigation efficiency and reduced demand through advanced irrigation systems, anticipating advancements in water management practices.

Scenario 1 tested the sensitivity on irrigation water use using an estimated 35% efficiency rate for the year 2021. In addition, a 0% value for decrease in irrigation demand was achieved via advanced irrigation systems as it is assumed that it would be less than 1% at the present time. The City of Cape Coral has thousands of automatic sprinkler systems that are extremely inefficient and were not installed properly leading to continued water waste. When the city's new conservation ordinance is fully implemented in December 2024, all new automatic irrigation systems can meet a ≥70% efficiency requirement. Scenario 1 should be considered the baseline scenario for the purposes of this research.

In the ‘Parameters’ field in the eRAMS software, the following city scenario input data were populated:

• In the Home Profile, average homes in 2016 used 522 LPHPD (138 gallons per household per day (GPHD)), 100% was selected and 10% of indoor demand is assumed to be consumed.

• The commercial, industrial, and institutional (CII) indoor demand per household (L/d; gallon/household), the percent of CII demand that is treated domestic wastewater is 20%.

• For the landscape irrigation demand and conservation, the following parameters were used: the temperature above which residents irrigate was set at 13.3°C. The average area irrigated percentages were as follows: 60% open space, 65% low density development, 35% medium density development, and 5% high density development.

• For domestic wastewater reuse, the portion of faucet water that is not considered wastewater was set at 50%.

• For wastewater reuse, the minimum percentage blended with treated raw water supply was set at 60%.

• For stormwater use, 90% of precipitation that turns into runoff was selected.

In the ‘Practices’ field in the eRAMS software, the following values were selected:

• The percentage of domestic wastewater available for indoor residential and outdoor reuse was set at 100%, and the percentage of domestic wastewater available for indoor CII reuse was set to 100%. Storage capacity and adoption field percentage were set to 0%.

• The percentage of stormwater available for indoor residential and outdoor capture and reuse was set at 100%, and the percentage of stormwater available for indoor CII reuse was also set at 100%. Storage capacity per household in gallons was set at 58 m³ (15,000 gallons) since the freshwater canal system has approximately 3.7854 × 10⁶ m³ (1 billion gallons) of storage within the 483 km (300 miles) of freshwater canals. In the City, the adoption field percentage for combined flushing and irrigation was set at 50%.

• The percentage of wastewater reuse available for indoor residential and outdoor capture and reuse was set at 100%, and the percentage of stormwater available for indoor CII reuse was also set at 100%. The adoption field percentage for combined flushing and irrigation was set at 50%.

• For irrigation conservation, the percentage of net irrigation requirement met was set at 45%. Decrease in irrigation achieved via advanced irrigation systems was set to 0%. Irrigation efficiency was set at 35% and the percentage of precipitation for which residents account when making an irrigation decision was set at 100%. A plant factor of 0.8 was set for annual flowers and bedding plants; general turfgrass lawns (cool season), home fruit crops; and deciduous vegetation. Plant factors are based on Simplified Landscape Irrigation Demand Estimation (SLIDE) rules (Kjelgren et al. 2016). SLIDE is a framework for designing and regulating water-efficient urban landscapes based on selection of appropriate plant factors in combination with lower density planting and hardscape.

• In the Projections fields, the population was set at 3%, household change was set to 0%, open area change was set to −2%, low density area change was set to 0%, medium density change was set to 0%, high density change was set to 0%, and imperviousness change was set to − 3%.

In the climate parameters section, the Parameter-elevation Regressions on Independent Slopes Model (PRISM) was selected as the climate source. PRISM is a spatial climate data set used by eRAMS software (PRISM Climate Group 2023).

• The minimum temperature change was set to 0%, maximum temperature change was set to 0%, average temperature change was set at 1%, and the precipitation change was set to −1%.

The IUWM model simulation utilized historical data from 2010 to 2018 for initial setup. Its runtime was 11.4 s, with a processing time of 130.7 s required for the model execution to conclude.

Scenario 2 tested the sensitivity on irrigation water use using an estimated 50% efficiency value and 25% value for decrease in irrigation demand achieved via advanced irrigation systems for the year beginning 2043. In Scenario 2, irrigation system efficiency increased by 15%. The value for increased efficiency via advanced irrigation systems was increased from 0% to 25%. The baseline parameters used for Scenario 2 are outlined below.

In the ‘Parameters’ field in the eRAMS software, the following values were selected:

• In the Home Profile, average homes in 2016 used 522 LPHPD (138 GPHD); 100% was selected and 10% of indoor demand is assumed to be consumed.

• In the CII indoor demand per household (L/household), the percentage of CII demand that is domestic wastewater is 20%.

• For the landscape irrigation demand and conservation, the following parameters were used: The temperature above which residents irrigate was set at 13.3°C. The average area irrigated percentages are as follows: 60% open space, 65% low density development, 35% medium density development, and 5% high density development.

• For domestic wastewater reuse, the portion of faucet water that is not considered wastewater was set at 50%.

• For wastewater reuse, the minimum percentage blended with treated raw water supply was set at 60%.

• For stormwater use, 90% of precipitation that turns to runoff was selected.

In the ‘Practices’ field in the eRAMS software, the following values were selected:

• The percentage of wastewater available for indoor residential and outdoor reuse was set at 100% and the percentage of wastewater available for indoor CII reuse was set to 100%. Storage capacity and adoption fields percentage were set to 0%.

• The percentage of stormwater available for indoor residential and outdoor capture and reuse was set at 100%, and the percentage of stormwater available for indoor CII reuse was also set at 100%. Storage capacity per household in gallons was set at 58 m³ (15,000 gallons) since the freshwater canal system has approximately 3.7854 × 10⁶ m3 (1 billion gallons) of storage within the 483 km (300 miles) of freshwater canals in the city, and the adoption field percentage for combined flushing and irrigation was set at 50%.

• The percentage of wastewater reuse available for indoor residential and outdoor capture and reuse was set at 100%, and the percentage of stormwater available for indoor CII reuse was also set at 100%. The adoption field percentage for combined flushing and irrigation was set at 50%.

• For irrigation conservation, the percentage of net irrigation requirement met was set at 45%. Decrease in irrigation achieved via advanced irrigation systems was set to 25% since it is anticipated that the proposed irrigation ordinance will increase in advanced irrigation systems. Irrigation efficiency was set at 50% and the percentage of precipitation for which residents account when making an irrigation decision was set at 100%. A plant factor of 0.8 was set for annual flowers and bedding plants; general turfgrass lawns (cool season); home fruit crops; and deciduous plants. Plant factors were taken from SLIDE rules (Kjelgren et al. 2016).

• In the Projections fields, population was set at 3%, household change was set to 0%, open area change was set to −2%, low density area change was set to 0%, medium density change was set to 0%, high density change was set to 0%, and imperviousness change was set to −3%.

In the climate parameters section, PRISM was selected as the climate source (PRISM Climate Group 2023).

• Minimum temperature change was set to 0%, maximum temperature change was set to 0%, average temperature change was set at 1%, and the precipitation change was set to −1%.

The IUWM model simulation utilized historical data from 2010 to 2018 for initial setup. The IUWM model compile time was 11.4 s, and processing time was 133.9 s for the model execution to finish.

Scenario 3 focused on the sensitivity on irrigation water use considering a 71% efficiency rate as Cape Coral is approaching its projected build-out (maximum development) around 2065. A 71% efficiency value represents an increase of 21% from the year 2043 Scenario 2 value. A 30% value was used for the estimated decrease in irrigation water used via advanced irrigation systems, an increase of 5% over Scenario 3. The final Scenario 3 is an estimate of the possible overall water savings that may be achieved in the future by the City of Cape Coral mandating that all new automatic irrigation systems meet the 70% or greater efficiency requirement. The baseline parameters used for Scenario 3 are outlined below.

In the ‘Parameters’ field in the eRAMS software, the following values were selected:

• In the Home Profile, average homes in 2016 used 522 LPHPD (138 GPHD); 100% was selected and 10% of indoor demand is assumed to be consumed.

• In the CII indoor demand per household (m³/household), the percentage of CII demand that is graywater is 20%.

• For the landscape irrigation demand and conservation, the following parameters were used: The temperature above which residents irrigate was set at 13.3°C was used. The average area irrigated percentages are as follows: 60% pen space, 65% low density development, 35% medium density development, and 5% high density development.

• For wastewater reuse, the portion of faucet water that is not considered wastewater was set at 50%.

• For wastewater reuse, the minimum percentage blended with treated raw water supply was set at 60%.

• For stormwater use, 90% of precipitation that turns to runoff was selected.

In the ‘Practices’ field in the eRAMS software, the following values were selected:

• The percentage of graywater available for indoor residential and outdoor reuse was set at 100%, and the percentage of graywater available for indoor CII reuse was set to 100%. Storage capacity and adoption fields percentage were set to 0%.

• The percentage of stormwater available for indoor residential and outdoor capture and reuse was set at 100%, and the percentage of stormwater available for indoor CII reuse was also set at 100%. Storage capacity per household in gallons was set at 58 m³ (15,000 gallons) since the freshwater canal system has approximately 3.7854 × 10⁶ m³ (1 billion gallons) of storage in the city's 483 km (300 miles) of freshwater canals and the adoption field percentage for combined flushing and irrigation was set at 50%.

• The percentage of wastewater reuse available for indoor residential and outdoor capture and reuse was set at 100%, and the percentage of stormwater available for indoor CII reuse was also set at 100%. The adoption field percentage for combined flushing and irrigation was set at 60%.

• For irrigation conservation, the percentage of net irrigation requirement met was set at 45%. Decrease in irrigation achieved via advanced irrigation systems was set to 30% since it is anticipated that the proposed irrigation ordinance will increase in advanced irrigation systems. Irrigation efficiency was set at 71% and the percentage of precipitation for which residents account when making an irrigation decision was set at 100%. A plant factor of 0.8 was set for annual flowers and bedding plants; general turfgrass lawns (cool season); home fruit crops; and deciduous plants. Plant factors are taken from SLIDE. SLIDE is aimed at stakeholders in urban landscapes who primarily design and regulate, but also manage, urban landscapes to use less water (Kjelgren et al. 2016).

• In the Projections fields, population was set at 3%, household change was set to 0%, open area change was set to −2%, low density area change was set to 0%, medium density change was set to 0%, high density change was set to 0%, and imperviousness change was set to −3%.

In the climate parameters section, PRISM was selected as the climate source (PRISM Climate Group 2023).

• Minimum temperature change was set to 0%, maximum temperature change was set to 0%, average temperature change was set at 1%, and the precipitation change was set to −1%.

The IUWM model simulation was configured to run with historical data utilized from 2010 to 2018 for initial setup. The IUWM model compile time was 12 s and processing time was 137.3 s for the model execution to finish.

Irrigation demands were determined by the Blaney–Criddle method to estimate the amount of irrigation water needed to support healthy turf grass growth in southwest Florida. An average of 776 LPCPD (205 GPCPD) was calculated (Table 1). This is similar to the average irrigation demand rate of 806 LPCPD (213 GPCPD) determined from the last 6 years of historical data. The maximum day rates by the two methods were 472,793 and 322,772 m³/d. The two methods differ on maximum day demand, which is where the city will likely see a shortfall in available irrigation water supply (MWH 2011). Irrigation demands were predicted to exceed the supply in 2011, based on the historical average usage for the period 2004–2009 (MWH 2011).

Based on the historical average and maximum day irrigation demand rates of 806 LPCPD (213 GPCPD) and 1,359 LPCPD (359 GPCPD), respectively, the current sources of irrigation water will not meet future demands (MWH 2011). The projected average day demands may exceed average day irrigation supply by 2025, with an average irrigation water supply deficit of 936,369 m³/d (8 MGD) by 2040 and 52,280 m³/d (11.5 MGD) at the build-out of the city.

A summary of projected irrigation water supply deficits for both average and maximum projected irrigation demands is provided in Table 2.

The study highlights the importance of evaluating the city's current and proposed water supply options to meet future irrigation demands. The current irrigation water flows may be augmented by several other local water sources or by available water management options (MWH 2011). There are five relevant potential options available to the city to augment the current irrigation water flows (MWH 2011). The potential water management options are (1) withdrawal from the water table aquifer, (2) make canal operational changes, (3) develop an aquifer storage and recovery (ASR) system, and (4) implement additional conservation management rules (MWH 2011).

The City of Cape Coral ranks potential irrigation sources based on feasibility and/or ease of implementation. Conservation management ranks highest for reducing irrigation demand and minimizing the need for additional water sources. Canal Operational Changes follow as cost-effective measures to enhance storage. ASR is third, offering large-scale storage but requiring more investment. Finally, the water table aquifer ranks lowest due to reliability concerns and saltwater intrusion risks. The ranking of identified water sources is provided in Table 3.

The City of Cape Coral recently updated the irrigation ordinance, which is designed to decrease peak irrigation demands and curb water waste through regulation of private automatic sprinkler systems. In the Summer of 2022, the city instituted demand management principals by adding additional irrigation schedule time slots and eliminating Tuesday as a non-watering day to reduce peak pressure demands and achieve more static average pressures during the three daily watering time slots (8 pm–11:59 pm, 12:01 am–4 am, 4:01 am–8 am). Since implementation, the city has been able to better maintain water pressures in the dual reclaimed water system in the 50 psi range, which is assisting with reducing water violators who believed they were not getting adequate pressure to water their lawns.

Due to the implementation of water efficiency measures and restrictions, the overall irrigation usage rate decreases progressively from Scenario 1 to 3. The key differences between these scenarios are that during the dry season, which typically begins in November and ends in May the following year, water demands can be decreased by increasing automatic sprinkler system efficiency and encouraging water conservation through regulation and enforcement.

The permitted surface water withdrawals from the City of Cape Coral freshwater canal system are currently 121,133.2 and 174,129 m³/day for average and maximum days, respectively. Reclaimed water flows at the build-outs of all the city water reclamation facilities have been estimated to be 140,060.3 m³/day. Cape Coral's irrigation demands ranged between 20 MGD and 55 MGD. Dry season withdrawals from the freshwater canal system are likely limited to 174,129 m³/day (maximum month) as currently permitted (MWH 2011).

The percentage of water used is the least between June and September and accounts for 26% of the total historical irrigation usage (MWH 2011). The dry season (October through May) accounts for 74% of historical irrigation usage during the year. MWH (2011) estimated future seasonal irrigation demands by using historical monthly usage as provided in Table 4. The irrigation water includes reclaimed water sent to the irrigation system from two wastewater treatment facilities (Southwest Water Reclamation and Everest).

The build-out population in the City of Cape Coral is estimated to be approximately 400,000 people. Therefore, by using a more conservative population increase of 1.5% per year for planning purposes, the year of build-out will occur in 2065, not 2080 as MWH previously estimated. Based on the updated 2065 build-out scenario as depicted in Table 5, the irrigation demand requirements are vastly different compared to the past projections. Recent historical demands correlate with a 1.21 m³ PDPC demand number rather than the MWH estimate of 2.27 m³ PDPC rate shown in Table 4. The 171,977 m³/day rate corresponds with city records for the average maximum day actual irrigation system demands occurring in 2021. Based on Blaney–Criddle, an average irrigation demand is projected to be 219,758 m³/day in 2065. Whereas irrigation demands using the verified 1.21 m³ PDPC demand scenario results in a use of 336,080 m³ PDPC.

The estimated build-out population in the City of Cape Coral is estimated at approximately 400,000 people. Therefore, by using a more conservative population increase of 1.5% per year for planning purposes, the year of build-out will occur in 2065, not 2080 as MWH previously estimated. Therefore, based on the updated 2065 build-out scenario depicted in Table 5, the irrigation demand requirements are vastly different than what MWH projected. Recent historical demands correlate with a 1.21 m³ PDPC demand number rather than using MWH's high value of 2.27 m³ PDPC shown in Table 4. The 171,977 m³/day value corresponds with the city records for the average maximum day actual irrigation system demands occurring in 2021. Based on the Blaney–Criddle method, an average irrigation demand is projected to be 219,758 m³/day in 2065, whereas irrigation demands using the verified 1.21 m³ PDPC demand scenario results in 336,080 m³/day.

The three eRAMS scenarios are limited in the ability to provide future irrigation system projections. For the purpose of this study, 8-year data were utilized to set up the model. The model simulation settings from Scenario 1 served as a basis for simulating a present or baseline scenario. Using Scenarios 2 and 3, irrigation conservation–related parameters were adjusted along with adoption rate percentage to demonstrate how increased conservation using advanced irrigation systems can decrease demands and increase conservation, which will begin in December 2024 and extend until the estimated build-out period (year 2065). In addition to adjusting population projections to reflect demographic shifts impacting water demand, the simulation integrated climate data, allowing for analyses that consider the effects of temperature and precipitation changes. Moreover, by incorporating technological factors like irrigation efficiency rates and the adoption of advanced irrigation systems, the scenarios were comprehensively analyzed. This approach offers valuable insights into potential water savings and assists in strategic decision-making for sustainable water management practices in the City of Cape Coral.

The city recently completed an interconnect pipeline with the Florida Governmental Utility Authority (FGUA) that allows them to purchase an average of 7,570.8 m³/day and if available up to 22,712.5 m³/day. This water originates in Lee County from wastewater customers located in North Fort Myers, Florida, and is treated to public access reclaimed quality water at the FGUA's North Fort Myers Wastewater Facility. Cape Coral is completing construction on a subaqueous 61-cm-diameter (24-inch) pipeline interconnect that will allow the City of Fort Myers, FL, South Advanced Wastewater Treatment Facility to send excess reclaimed water to the City of Cape Coral. The project is designed to deliver up to 45,425 m³/day of treated wastewater. The interlocal agreement executed between both cities requires the City of Fort Myers to deliver a minimum of 22,712.5 m³/day by 1 January 2024. During 2021, the City of Cape Coral entered into a 3-year agreement with the owner of a freshwater reservoir (former mining pits) located near U.S. Highway 41 in Charlotte County, FL. The agreement provides that the City of Cape Coral will construct a dedicated pipeline and pumping station that has the capability of providing approximately 60,567 m³/day of surface water that is stored in the reservoir. Currently, the City of Cape Coral has needed to pump water during the dry season months to recharge the freshwater canal system since the canal pump stations cannot operate below a water level altitude of 1.2–1.5 m (4–5 feet) (National Vertical Geodetic Datum (NGVD)). In 2020, the City of Cape Coral was successful in obtaining a 20-year water use permit from the Southwest Florida Water Management District (for Charlotte County water use). The permit allows the city to pump 60,567 m³/day of additional water to recharge the canal system in Cape Coral.

It is imperative that the City of Cape Coral explores all options to meet future drinking water and irrigation water demands. Since sources of fresh water are limited, the City of Cape Coral adopted a new watering restriction ordinance on 7 June 2023, which is voluntary until 1 December 2024, when it will go into effect that requires more efficient irrigation systems. The new ordinance will require all new automatic irrigation systems to meet a minimum of 70% efficiency or greater efficiency threshold. It is anticipated that it will decrease outdoor irrigation demands by approximately 16% or more. The new ordinance created an additional nine watering time slots to better distribute demands and reduce operational impacts to the irrigation transmission and distribution system. Some of the incentives being considered include a $500 reduction in irrigation impact fees and will allow advanced irrigation systems a variance from the 2 day/week watering restrictions if a smart and efficient automatic irrigation system is installed, including a smart weather-based controller with soil sensors. These types of advanced irrigation systems will only turn on automatically when the soil and plants require water. Most of the new advanced irrigation system controllers are connected wirelessly to home Wi-Fi systems, and they can automatically adjust a watering schedule based on local weather data and local water alerts and restrictions. The systems can be operated from a mobile phone, and some are compatible with the Amazon Alexa application. The cost of this technology is relatively inexpensive. Some systems claim to save as much as 50% of water previously used for outdoor irrigation purposes.

According to Figure 6, the City of Cape Coral will have enough supply sources to provide irrigation-quality water to its customers if a 1.21 m³ PDPC usage level is not exceeded. If a 2.27 m³ PDPC usage level occurs, the city will need to acquire 288,505 m³/day of additional water sources to meet a total of 630,498 m³/day demand.

In the absence of water shortage threats, peak demands (a term commonly used to designate periods of very high demand) are a conventional infrastructure management challenge. Water treatment plants, storage systems, and distribution networks must be sized to meet these temporary surges in demand, resulting in higher design and maintenance costs for systems that are oversized for most of the year (Burn et al. 2002; Kanakoudis 2002; Lucas et al. 2010; Beal et al. 2016). Curbing seasonal and short-term peaks in water demand has emerged as a key strategy for promoting adaptation to urban drought risk, and recent work has pointed to the potential of outdoor water conservation generally, and restrictions on irrigation water use specifically, as promising tools for achieving this goal (AghaKouchak et al. 2015; Gober et al. 2015; Breyer et al. 2018). Multiple studies have revealed that overirrigation of urban yards is common across climate types, leaving ample room for conservation (Endter-Wada et al. 2008; Romero & Dukes 2008; Survis & Root 2012; Glenn et al. 2015; Litvak & Pataki 2016; Chini & Stillwell 2018).

The proposed outdoor water management by the City of Cape Coral incorporates outdoor watering enforcement, a night watering schedule, and fee incentive programs. Limited research is available to quantify or establish the impact of integrated night schedules, incentives, and permanent restrictions on outdoor water use, warranting further study.

The reuse of treated wastewater supplemented by the use of canal water to meet irrigation demand has large economic benefits. Since the City of Cape Coral must use the desalination of brackish water to meet the municipal system demands, the reuse system eliminates the need to burden the drinking water system with the irrigation demand. The source aquifer system beneath the city that is used as the raw water source for the municipal water supply system has a limited sustainable yield (Harvey & Missimer 2020; Pearson et al. 2021). If the reuse system had not been constructed and used, irrigation would have had to be supplied via the municipal system, which would cause considerable added cost to develop additional desalination capacity. These costs could raise utilities by over 50%.

As water and wastewater utility operations mature, managing automatic irrigation systems and outdoor water use will be key in providing sufficient water supplies and meeting peak domestic use and outdoor water demands in the future. Water and wastewater utilities should adopt strict policies and enforce them if they are to be successful in managing growth. In addition, dual water systems that utilize reclaimed water and other fresh water sources are vulnerable to changing seasonal weather patterns, and the key to providing reclaimed water system reliability can be achieved by providing significant water storage for use during dry seasons.

This study demonstrates the importance of scenario analysis in effective water management. The findings from the eRAMS IUWM demonstrate that enhancing the efficiency of automatic irrigation systems can lead to substantial water savings, significantly reducing peak demands. The simulation results indicate a potential reduction of over 50% in peak water use for the month of April. Scenario 3 mandates that all new automatic irrigation systems achieve 70% or greater efficiency, resulting in significant water savings through enhanced conservation measures. During the month of April, simulated peak water use dropped to 4,542,495 m³, and in August, the total water use was 1,816,998 m³/day.

Managing the installation of automatic sprinkler systems can provide significant benefits to the utility and its customers in the form of affordable rates and deferred capital improvement costs. The cheapest form of new water supply can be found through conservation. Maximizing the reuse of domestic wastewater is essential for the City of Cape Coral, particularly in light of increasing irrigation demands, environmental concerns, and limited water resources. The city's historical reliance on antiquated irrigation systems has necessitated a shift toward more efficient practices. By implementing year-round water use restrictions and diversifying water sources, including the use of brackish groundwater and full reuse of wastewater, Cape Coral has made significant strides in water management.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.