Freshwater requirement to attain open-defecation-free status in Nigeria by 2025

Nigeria is a signatory to the United Nations Sustainable Development Goals (SDGs). Target 6.2 of Goal 6 has requested countries parties to the SDGs to end open defecation by 2030. Notwithstanding this, the Government of Nigeria launched a far more ambitious National Road Map in 2016 to end open defecation in the country by 2025. Since water and sanitation are inextricably linked, this paper estimates Nigeria ’ s freshwater requirement to attain open-defecation-free status by 2025. The analysis revealed that the quantity of freshwater required amounted to between 2.74 and 2.94 × 10 6 cubic metres (m 3 ) per day or between 1.0 and 1.1 × 10 9 m 3 per year under the assumptions made. This amount is relatively less than Nigeria ’ s total water resources potential estimated at 375.1 × 10 9 m 3 /year. The data presented will help increase the reliability of estimates of water for sanitation in Nigeria.

Nigeria's water resources potential is estimated at 332.7 × 10 9 cubic metres (m 3 ) of surface and 155.8 × 10 9 m 3 of groundwater (FRN ). Despite this relatively abundant water resource, there are still cases of freshwater shortage during the dry season, especially from December to April, when some streams and rivers run dry. The total water use (for irrigation, freshwater aquaculture, livestock, and municipal) is projected to increase from 5.93 in 2010 to 16.59 × 10 9 m 3 /year in 2030. The municipal component, 3.1 × 10 9 in 2010, is expected to rise to 8.9 × 10 9 m 3 /year in 2030 (FMWR b). In Nigeria, the provision of drinking water falls within the constitutional responsibility of the State Governments (Adeoti & Fati ). Available data indicated that country-wide access to piped water was 11% in 2017. Roughly 8% of the rural population and 15% of the urban population had access to piped water in 2017 (UNICEF and WHO ). Water and sanitation are positively linked. Water is needed to flush, for anal cleansing, handwashing and toilet cleaning. As one of the major indicators of extreme poverty (Abubakar ), eliminating open defecation has benefits from the health, nutrition, learning, social and economic perspectives (FMWR a).
To realise this still poses some challenges on water resources management, especially in developing economies.
Literature investigating the amount of water needed for human faeces disposal remains sparse, at least from the Nigerian perspectives. Studies related to water and sanitation in Nigeria have focused on inequalities in households' environmental sanitation practices, looking at the case of Ile Ife (Faniran & Ojo ), impact and sustainability of community water supply and sanitation programmes in Nigeria (Ademiluyi & Odugbesan ), spatial variations in access to improved sanitation and water, using the local government areas in Lagos state as a case study (Kunnuji ), drinking water quality, household sanitation, and hygiene practices in Tunga Magaji, a rural  latrines, pit latrines with(out) slab, and composting toilets.
'House', as used in this study, refers to a complete standalone residential building. Its use in this study differs from household which refers to a family unit. In Nigeria, two or more families (or households) may inhabit one house and share the same toilet. How many of these exist in Nigeria is not known. However, using the house as the unit of analysis makes it easier for data collection and analysis (for example, to quantify the amount of water used for toilet cleaning).

METHODOLOGY Sites selection
To understand the types of sanitation facilities-in-use and the amount of freshwater required, Ado Ekiti and Osogbo, both located in the southwestern part of Nigeria, were purposely selected. The selection of these sites was favoured by ease of data collection and financial constraints. Limiting the study to two urban sites was deliberate and informed by financial

Data gathering
To identify the types of toilet facilities being used and the amount of water required, a face-to-face questionnaire survey was administered to some residents of the selected sites ( Table 2). The survey was carried out between June and August 2019 under conditions of confidentiality and anonymity (the Institution has no Ethics Screening Committee. However, it is expected that researchers comply with good ethical practices when dealing with human subjects.
For example, obtain informed consent, provide anonymity and confidentiality assurance). Because of the purpose of this study, houses were purposely selected. The selection criteria were that houses had the time and were willing. These houses were verbally invited to participate in the study. Purposive sampling was deliberately adopted to capture the various sanitation end-use facilities in the face of limited financial resources. Besides this, houses using two or more different types of toilets were eliminated from the survey, because they could make the script complex and data difficult to analyse. Based on this and other associated problems (coinciding with the time of the survey was

DATA ANALYSIS
This study aimed at identifying the various onsite human faeces disposal facilities and estimating the amount of water used during faeces disposal, with the objective of conducting a quantitative analysis on the data collected.
Descriptive statistics (mean, standard deviation, and percentages) was used to analyse the data collected.
In the analysis, the study adopted a four-scenario analysis (Table 3) to quantify Nigeria's freshwater requirement for sanitation and end open defecation by 2025. This is because there was no specific trend or known pattern of adoption to predict the future use of sanitation facilities in Nigeria (see Table 1 when compared with that of the base year at 23.9% (Table 3). This also agrees with the assumption of the National Road Map towards making Nigeria open-defecation-free by 2025 (FMWR a). However, the National Road Map was silent on the proportion of the population using other unimproved sanitation facilities such as pit latrines without slab, hanging toilets, bucket toilets, etc.
(  Table 3). Nevertheless, Nigeria plans to achieve a country-wide access to safely managed (or improved) sanitation by 2030 (FMWR a).

LIMITATIONS OF THE STUDY
Although the study has adopted a purposive sampling method for primary data collection to minimise data  personal hygiene after urinating (for example, in houses using wet toilets or dry toilets). Further study is required to determine the amount of water use associated with urinating.

RESULTS AND DISCUSSION
The results of the survey revealed that 16.2% of the houses As illustrated in Figure 3, the overall mean values per person per defecation were 10.7 ± 2.9 L for flushwater, 1.7 ± 0.4 L for anal cleansing, 1.6 ± 0.5 L for handwashing, and 3.8 ± 1.6 L for cleaning per person per day. The value   Combining the data in Figures 2 and 4 together, overall, as shown in Figure 5, houses using FT 1 accounted for the highest water use, 195.6 L per day. Besides being the highest flush water user (see also Figures 2 and 3), another reason for this is that FT 1 had the highest mean number of persons per house (8.2 ± 3.9) compared with VIP (7.5 ± 2.6), PL (7.3 ± 3.6), OD (7.0 ± 4.1), PF (6.7 ± 2.6), and FT 2 (5.5 ± 3.1). The absence of metering in most piped houses in the surveyed sites may have accounted for the high water use in FT 1 . The overall average house size (including infants) obtained in this study amounted to 7.03 ± 3.32 persons per house per day.
Considering the information provided in Figures 2 and 4 together, the sanitation water use tree that formed the basis of quantifying the amount of freshwater needed by 2025 under the various end-use sanitation facilities tThese facilities are: Pour/Flush, VIP latrine, Pit latrine with slab, Composting toilet, and unimproved toilet (from Table 3)) is shown in Figure 6. Using the overall average values  (Table 4), or between 1.00 and 1.07 × 10 9 m 3 per year. In the analysis, the overall average defecation frequency used was 1.0. To estimate the average number of houses by 2025 (see  Table 1)) toilets are not water-based systems, their water use was roughly assumed to be similar to that of pit latrines with slab. The expected Nigeria's total population by 2025 used in the calculation is 239.874 million (see Table 3). The water use rate (that is, the ratio between total water demand and Nigeria's total water resources potential, estimated at 375.1 × 10 9 m 3 /year (FRN )) by 2025 translated to between 0.27 and 0.29%. This reveals that the total freshwater demand to attain open-defecation-free status in Nigeria is much less than the country's total water resources potential.
However, as shown in Figure 7, pour/flush toilets represented the highest consumer of water for sanitation, majorly influenced by the flush water requirement. This indicates that climbing the sanitation ladder as suggested by the

CONCLUSIONS
This study concludes that the amount of freshwater required to realise Nigeria's open-defecation-free status by 2025 amounted to between 1.0 and 1.10 × 10 9 m 3 under the assumptions made. This represents between 0.27 and 0.29% of Nigeria's total water resources potential estimated at 375.1 × 10 9 m 3 /year. Although this requirement is not huge compared with the estimated total water resources potential, to even out water supply, especially during the dry periods when freshwater shortages are expected, will require considerable investments in water storage and supply systems.
This will require the joint efforts of both the federal and the state governments in Nigeria. Notwithstanding its limitation, the outcome of this study is useful in the field of water, sanitation and hygiene (WASH) in Nigeria and elsewhere.    Table 4).