The WHO Guidelines provide the basis for drinking water standards built around the framework for safe drinking water in which prevention of contamination is the key component. The pressure to conserve and protect water has resulted in the need to reuse treated wastewater. This is can help protect source water quantity and quality, under threat from urban and population pressure and climate change. Emerging contaminants found in wastewater from human activity at a personal, domestic and industrial level are a barrier to reuse and a concern for source water quality. Control at the ultimate source is difficult, suggesting that a new approach to the whole managed water cycle is required. Monitoring is difficult and expensive, so traditional regulation is not useful. The best point of control appears to be wastewater treatment so it is appropriate to develop technology standards with operational monitoring to deliver the necessary quality of treated wastewater. However, this requires long-term planning and investment.
Pressure on water resources continues to grow as the demands on water increase with an expanding world population. This demand includes water for drinking and agriculture, but also for other domestic and industrial purposes. As urbanization grows along with an increased standard of living, these ancillary demands expand significantly both for domestic and community activities. The other side of the problem is dealing with the sewage from large and growing urban populations, and that is complicated by the growing number of substances that are used to support modern living, including cleaning materials, pharmaceuticals and other personal care products. Dense populations also mean the presence of large numbers of pathogens, which will be greatly exacerbated by outbreaks of disease.
These pressures can adversely impact on the quality of water in both surface and groundwater sources, through over abstraction and also by the introduction of a wide range of pollutants. There is also a tension between the demands of ever larger cities and the needs of small rural communities.
If this was not enough, climate change is introducing significant levels of uncertainty regarding rainfall patterns, with many more extreme events, both in the form of drought and also extremely intense rainfall (Trenberth 2011). Even in temperate climates, these events are being seen. Both can impact significantly on source water quantity and quality, and drought followed by intense rainfall can have even more severe effects on water quality, introducing more contaminants to surface water. Groundwater can suffer from the impact of water levels falling during drought, resulting in oxidation of minerals to form different (oxidized) species which are then dissolved on recharge.
While the approach has been to regulate the quality of water by standards covering individual microbiological, chemical and physicochemical parameters for drinking water, and more basic standards for surface water and wastewater effluent, the pace of change suggests that this will not be enough in the future, and that it will be necessary to think more holistically about how water resources are regulated and managed.
WATER SOURCE CONSERVATION
Using less water, by more efficient and less wasteful water use, is an important part of the conservation strategy, but this is not enough to deal with a problem that continues to grow. Moving water from regions with more than enough water to regions without sufficient water can be extremely difficult and prohibitively expensive. Such transfers are also vulnerable to political interventions and to pollution, over which the user community has no control. Water is heavy and so, for economic transfer, requires appropriate geography to allow flows over long distances. Equally, capture of water at times of excess in order to store it for times of shortage requires considerable planning and care not to cause quality problems for existing sources. The areas of storage required can be very large and this introduces competition for other land uses. Singapore has achieved this by building the Marina Barrage for which there may yet be significant issues for managing water quality in the future. In the UK, suggestions for building a new reservoir to supply the water stressed South East have met with considerable public opposition. All of these issues mean that we will probably have to develop a range of strategies and one of those is reuse of treated wastewater. Already reuse schemes are in progress and many more are planned. National and international bodies, including WHO, are looking to develop standards and guidelines that will help to facilitate acceptance of reuse and increase confidence to invest in such schemes. For a number of countries, there is little choice and reuse can provide a more cost-effective option than desalination. Spending money to dispose of wastewater and then spending even more to treat other sources makes little economic sense when the treatment processes for the latter can easily be used to manage the former and return it to use safely. Already wastewater is being considered as a basic resource, and the recovery of nutrients and other resources is now becoming economically feasible.
Wastewater can be treated centrally, as is primarily the case at present, or locally, as new technologies for toilets are developed. Both centralized and local systems can provide biosolids and treated wastewater that can be reused, but it is probable that there will need to be a mix of the two in future.
Wastewater reuse can provide a number of ways to help in source conservation. Treated and, unfortunately, untreated wastewater have been discharged to surface waters for centuries; in some cases augmenting flows and in other cases returning abstracted ground- and surface-water to surface waters, but not always the same waters from which they were abstracted. Often the sources to which wastewater is discharged are abstracted for irrigation or drinking water, so the wastewater is actually reused but this is unplanned, with no real thought given to quality and the impact on quality. In many cases, the solution for drinking water abstraction from such waters has been to increase the sophistication of drinking water treatment in order to protect drinking water quality but this does nothing to protect source water quality.
Some efforts are made to control contamination entering surface- and ground-waters. Surface water, in particular, is difficult to protect without proper, long-term strategies because the changes necessary can require significant investment and extensive cooperation from polluters, such as agriculture and industry.
The historical use of combined sewers and storm drains is an example of an approach that is not suitable for highly urbanized areas when there are more frequent extreme rainfall events, because these cause overflows of diluted but untreated sewage. Efforts are being made to deal with these problems but it requires much more concerted planning and investment.
However, wastewater is also a resource that can be used in a variety of ways to help to protect water sources, particularly by providing a means of minimizing the use of drinking water or high-quality drinking water sources for purposes that do not require the same level of quality. The advantage of such an approach is that the level of treatment can be adjusted to the requirement of the uses or alternatively the uses can be tailored to the quality of wastewater available. This leads to a range of interesting possibilities, some of which are already being exploited in a number of countries and are a feature in the Middle East and in the Olympic Parks in both Sydney and London. Not only can wastewater be used for irrigating both food and non-food crops, it can also be used for municipal irrigation and other municipal uses, such as water features, lakes and wetlands. This last also provides a treatment process and so a double benefit. It can be used for industrial purposes and even domestic uses not requiring drinking water quality. Clearly, there are barriers to overcome and that is where regulation has a vital role to play. The issues surrounding the overall subject of wastewater re-use were considered at length in the Water Research Foundation/WateReuse Foundation/UKWIR project on a Framework for Developing Water Reuse Criteria with Reference to Drinking Water Supplies (Fawell et al. 2005) and there are excellent examples of successful reuse projects (Lazarova et al. 2013).
EMERGING CONTAMINANTS AND SOURCE WATER QUALITY
While we thought we knew a good deal about contaminants in source water the steady advances in analytical techniques have enabled us to detect and measure substances at extremely low concentrations that would not have been thought possible only a short time ago. These emerging contaminants, some of which have now been known of for over 10 years and might be better described as contaminants of emerging concern, consist of natural and synthetic hormones and other chemicals with endocrine disrupting capability, pharmaceuticals and personal care products. This last group is very diverse and includes such items as toiletries, cosmetics and household cleaning materials, all of which contain a number of constituent chemicals in varying amounts (Fawell & Ong 2012). While some of these substances are known to be present at microgram per liter concentrations in surface source waters, the majority are present at much lower nanogram per liter concentrations.
The concentrations in raw sewage will be reduced by wastewater treatment, and the concentrations in surface waters will be further reduced by physicochemical and biological processes, while drinking water treatment will also reduce concentrations. However, the reduction in concentration varies substantially between different substances, and groups of substances, in different treatment processes, and a significant number are not easily removed at all by the commonly applied technologies. Some will be broken down to substances of no concern, sometimes to carbon dioxide and water, but others will yield substances that are still of concern. For example, the breakdown of a range of products, including fire-fighting foams, which used perfluorinated compounds as building blocks, results in the release of these molecules which are more toxic, water soluble and persistent than the products in which they are incorporated. These are now causing severe localized problems in groundwater because they are so difficult to remove.
The significance of some of these emerging contaminants in drinking water has been considered. For example, WHO has produced the report of an expert panel on pharmaceuticals in drinking water (WHO 2011a). However, many of the substances, including personal care products, remain to be studied and relatively little is known about their presence in water. In terms of health effects from consuming drinking water, the conclusion of the WHO panel and several subsequent studies was that there is no immediate concern for health, at least from pharmaceuticals. However, that does not suggest that there is no concern in the long-term, and that we can forget about the issue, but it does suggest there is time to consider what to do and to plan for appropriate and long-term action. Until more is known about the presence and concentrations of many of these substances, other than the pharmaceuticals, no conclusions can be drawn about them and, although it is probable that the same conclusions could be drawn, uncertainty remains. To this must be added the probability that, in future, new contaminants of potential concern that are currently unrecognized/unknown will emerge as analytical techniques improve and new developments in manufacture emerge. The situation over the potential for adverse impacts on aquatic life is much less clear. Adverse effects of endocrine disrupting chemicals from wastewater have been shown in individual organisms but, apart from a small number of specific circumstances, effects on the stability of populations have not been demonstrated. However, the concentrations of some pharmaceuticals and other emerging contaminants are close to those that have been demonstrated to have adverse effects on aquatic organisms in the laboratory. In addition, there is an issue of the impact of a mixture of substances that can add up to an increased stress on aquatic populations. How much of a real impact these contaminants are actually having is not clear but, as with changes in climate, the combination of stressors may be sufficient to cause major impacts on aquatic populations and ecosystems. Microbiological contamination of water has been recognized as a significant problem for over a hundred years and has been responsible for many outbreaks of diseases such as cholera and typhoid. Today there are still significant numbers of people who suffer morbidity and death as a consequence of these waterborne diseases. Even in highly developed and wealthy countries, a lowering of guard can result in such outbreaks, although different organisms are usually involved.
Microbial contaminants come from animals and humans. In the case of the latter, sewage is a major source simply because organisms are excreted in feces. In addition, many of these microbial contaminants will be human pathogens and, when there are outbreaks of disease in the population, the numbers of particular pathogens will be greatly increased. Wastewater is, therefore a significant potential source of pathogen contamination of source waters that can impact on drinking water, bathing water and, potentially, fish and other food taken from such sources. Pathogens are also a concern when the source water is used for irrigation of food crops, particularly those that are eaten uncooked.
A number of pathogens have emerged as concerns for water in recent years. The outbreak of disease caused by Escherichia coli O157 in Walkerton, Canada, following a failure in chlorination in 2000 (Hrudey et al. 2003) was an important wake-up call. There are also other pathogens and opportunist pathogens, such as adenovirus and Campylobacter (WHO 2011b), that can be found in water and which may be responsible for at least a contribution to the background level of disease in the population.
Another microbiological issue which is of emerging concern is the presence of antibiotic resistant organisms. These will primarily be present as a consequence of their excretion by humans who have been taking antibiotics while resistant organisms from antibiotic treated livestock will enter the wider aquatic environment. In biological wastewater treatment systems, such as activated sludge, these bacteria are in close contact with many other organisms and can pass on the genes for resistance by conjugation, when the plasmids containing the genes are passed between bacterial cells. This can even happen if the cells are from different genera (Korzeniewska & Harnisz 2013). While there is little concern for properly treated drinking water, they are of wider concern because they may infect humans through poorly treated water or by other routes, including bathing and consuming irrigated food, in the same way as non-resistant organisms. However, it will no longer be possible to rely on antibiotics to treat the problem in infected individuals.
REGULATION, STANDARDS AND GUIDELINES
The traditional approach to regulation of surface and drinking waters has been to develop a set of numerical standards for microbiological, chemical and physicochemical parameters that can be monitored to show that the water body or drinking water is ‘safe’. A more limited range of chemical and physicochemical parameters is usually applied to treated wastewater effluent to reduce the risk of deterioration of receiving waters. The success of these approaches depends on ensuring that all of the key parameters are covered, that monitoring is appropriate in quality and frequency, and that standards are enforced by regulators because standards do not mean anything if they are not adhered to. Long lists of substances included in standards can lead to a false sense of security, particularly if there is inadequate monitoring or lack of enforcement, while highly precautionary standards may give the illusion of added safety, but will either be ignored or divert resources away from what is really important. In addition, standards without a clear practical purpose are a source of added cost without any benefit. However, one of the biggest drawbacks of the traditional approach is that it measures quality after the water has been supplied or discharged, and in this respect, it is actually designed to measure failure rather than prevent it.
WHO (2011b) in its Guidelines for Drinking Water Quality has developed a framework for safe water that is centered round drinking water safety plans. This approach is designed to identify potential hazards at each stage of a supply and put in place preventive measures that are monitored to ensure that they are working properly. These measures may be technology-based or based on good practice and common sense. This proactive, preventive management approach can be just as successfully applied to all parts of the managed water cycle including wastewater management and the reuse of treated wastewater. Drinking water safety plans require that, as far as possible, prevention should begin in the catchment to prevent contamination at source. As more is learned about the emerging contaminants, it is apparent that prevention of contamination at source will require a new approach to the managed water cycle and, particularly, to wastewater treatment. Intervention at this point helps to protect aquatic ecology and other uses of the water, including drinking water. Of course, there are other sources of contamination that will be preventable to varying degrees but prevention is usually much more cost-effective in the long-term.
This means that to properly manage water and wastewater to achieve the maximum advantage requires consideration of the whole managed water cycle and the various uses, which require different levels of quality to assure the safe use of water for drinking, bathing, irrigation in agriculture, horticulture and urban settings, and for use in such municipal features as fountains and lakes, are that quality and quantity can be managed with the minimum of added treatment. In terms of irrigation, it also means that source water quality in rivers and lakes will be improved. While only limited attention is paid to irrigation water quality from such sources at present, it will be increasingly important in future. However, one of the biggest advantages is that preventing problems increases public confidence in drinking water, bathing water and reuse of treated wastewater.
The greatest barrier to progress in this direction is the lack of long-term planning in most countries, because improving wastewater treatment will require significant investment and in many cases replacement of a good deal of existing infrastructure. While this has been increasingly easy to achieve for drinking water treatment it has not been the case for wastewater treatment in most countries. An additional barrier is the need for a rethink about the way in which we treat wastewater. New approaches, such as membrane bioreactors are providing a strong basis for moving forward with techniques which can be made more energy efficient and sustainable, but the need for research and development on wastewater treatment is pressing.
To achieve all this requires much more coordinated thinking on the managed water cycle that transcends the responsibilities of individual ministries, with regulation that starts to address the whole cycle. In addition, there is a need to think more creatively about regulation so that it more closely follows the principles of the WHO water safety plans applied to the whole managed water cycle, perhaps safe water management plans, in which water and wastewater safety plans are an integral part, and which include drainage and run off. That does not mean abandoning traditional standards. Indeed numerical standards are still important as they provide the targets and benchmarks for what the treatment processes need to achieve. Indeed, there may be a requirement for a broader range of standards to assist in process design and management. However, there is also a need for more operational parameters that can be monitored, often continuously, to show that the technology/processes of choice are working at their optimum at all times and, when the processes begin to move out of specification, point to the appropriate corrective actions. Such an approach seems to be essential to start to address the problems that surround city growth. That means that routine monitoring of a wide range of parameters is less important and such monitoring can be carried out less frequently as a final verification or audit step.
The requirement to consider the whole of the managed water cycle is being forced by population growth, urbanization and climate change. The polluted water courses and drinking water of the nineteenth century are now far in the past but the journey is not complete. John Snow showed the importance of separating sewage discharge from drinking water abstraction in the mid-nineteenth century, applying what the Romans knew in the first century. Now the pressures have increased and the need is not only for clean drinking water, but also to conserve and manage all waters. City-states like Singapore have shown the way with advanced technology and long-term planning, but thought is also needed about ways to apply this approach in less wealthy states. However, proper management of water and wastewater and the associated infrastructure is a cornerstone of development and will bring significant benefits to developing, as well as developed, countries. A new approach and more creative thinking are required for the next stage of the journey, and to provide a negotiable route into the future requires long-term planning. The process of regulating the whole of the managed water cycle with a more holistic and creative view of regulation must start now, following the examples of those countries that have already begun to move in this direction.