This special issue of Environmental Science and Pollution Research highlights selected papers presented at the Fourth Annual Water Efficiency Conference (7–9 September 2016, Coventry University, UK) which focused on developments in water management technologies and systems applied to water efficiency. This included approaches at all scales, from individual buildings to efficiency in water use and management through the whole water cycle, and involves research from across disciplines from the social to the physical sciences, representing a truly multi-, trans- and cross disciplinary area of study.
Originally set up in 2011, then funded by Defra, the Water Efficiency Network provides a forum to collaboratively explore the supply, treatment, distribution, risk monitoring, improved efficiency, management and conservation of water. It also investigates challenges in improving the adaptive capacity of building users, providers and professionals and consequently facilitate long-term, adaptable water efficiency through behaviour change and the use of technology. Its brief includes the harvesting of rainwater, reuse of greywater and the sustainable, efficient management of storm water. Papers in this special issue therefore reflect the efficient management of water at all scales, applied to many contemporary issues of concern and involve the inclusion of users and communities in participatory research.
As is clearly stated by Miereles et al., in order to improve the sustainability of water consumption, the concept of water efficiency has become increasingly important. When introducing new technologies and new ways of doing things, they need to be flexible in use and multiple benefits; in this way, they can provide added resilience to the system, improving sustainability and effectiveness. However, if the end-user does not engage with them or understand how they should be used, or is simply not interested, then, it is unlikely that they will be taken up to eventually become the normal way of doing things. Miereles et al. examined a specific approach in the University of Aveiro, Portugal, in which they trialled four different types of aerators in toilet washbasin taps which provided various discharge reductions. They found that user factors controlled how much water could be saved based on a comparison of water saved versus reduction in discharge of water from the tap, dependent on user comfort and water efficiency, resulting in less water savings in comparison with discharge reductions.
Reducing the amount of potable water use can also be achieved by utilising alternative water sources, and whilst approaches such as rainwater harvesting (RWH) and greywater reuse (GWR) have become increasingly used in the commercial sector, they have yet to achieve such a level of popularity at the individual household level. Sousa et al. investigated pay back periods and non-potable water savings in shopping centres in both Portugal and Brazil. Whilst technically, the design and installation of RWH in such commercial situations is relatively straightforward, with calculations available to determine tank volumes; it was found that the main factors driving the payback period were investment costs and water fees which were country-specific. Oviedo-Ocana et la., on the other hand, surveyed 35 high water using households in Columbia assessing the potential for RWH and GWR designed by the occupants themselves. The selected design afforded savings in drinking water use of 44% and a return on investment of 6.5% with the payback estimated at 23 years. This is in comparison with the findings of Sousa et al., whose savings varied between 60% in Portugal, paying back in 19 years, whereas in Brazil, the savings were between 20 and 50% but with a pay back of only 2 years as investment costs were lower, and water fees higher. The challenges around large scale implementation of RWH schemes which are efficient and multiple purpose were examined by Behzadian et al., by modelling the installation of a “smart” system which was proactive in controlling water level in the storage tank such that sufficient capacity was always available in order to contain rainfall from subsequent storms. The outcome of this modelling exercise found that the harvested rainfall could be used not only for non-potable uses at the household level, but also by providing volume to store storm water; local flooding could be reduced as excess would be released slowly to the storm water sewer system. RWH and GWR therefore have the potential to reduce potable water use, but a third type of water is generally wasted and that is storm water which is currently directed into the storm sewer system (SSS) and thence to the Waste Water Treatment Plant (WWTP). If it could be harvested, it would reduce the volume of water in the SSS and reduce flooding, and also reduce the expense of treating it at the WWTP. It could be used for non-potable activities, but there may be risks associated with this. Lundy et al. assessed these risks using a source-pathway-receptor model for the common bacterial pollutant in storm water, E. coli. Their findings indicated low to medium risk for most uses apart from car washing and the irrigation of raw edible food crops indicating the potential for storm water collection, but also the need for some form of treatment under certain scenarios.
Much of the research presented so far focused directly on water use and consumption, reducing potable water use. Other researchers took a wider approach, for example, Ip et al. examined the efficient use of waste heat generated by several showers installed in a Sports Centre at the University of Brighton, UK. They found that heat recovery from these 8 showers had a seasonal thermal effectiveness of more than 50% by recycling the heat to preheat incoming cold water. In terms of carbon pay back, accounting for the extra greenhouse gas emissions from the waste water heat exchangers, this was estimated to be achievable in less than 2 years. For life cycle costs, it was recommended by Ip et al. that this approach would benefit from heat recovery from fewer units to improve financial viability.
In order that the maximum benefits are gained from the use of water efficient technologies, they should have multiple roles in whatever system they are designed into. Two of the papers sought to improve the efficiency of drainage devices at the microbial level, and also provide benefits beyond just drainage. Firstly, using small-scale models, Coupe et al. modified a sustainable drainage system (SuDS) device, an infiltration or pervious paving system (PPS) and applied it to a landfill site where it would not only provide enhanced drainage capability and a vent for ground gases, but also include an active microbial layer where methane would be oxidised and essentially removed. Methane is a greenhouse gas and can pollute groundwaters; thus, this approach would make use of a water efficient drainage device to reduce contamination in the environment. The second project by Theophilus et al. focused on a different type of drainage device, this time in the roadside environment, the filter drain, which runs alongside motorways and main roads in the UK. These are essentially aggregate-filled ditches which collect road runoff, slowly conveying it to the receiving watercourse. Their purpose is to protect the asset by conducting water away from the road structure and prevent the road flooding, thus protecting the road user. However, as explained by Theophilus et al., this water is contaminated by traffic-associated pollutants such as hydrocarbons and large amounts of total dissolved solids. Whilst percolating through the aggregate in the filter drain, a certain amount of treatment is afforded by the process of biodegradation due to the development of a biofilm on the aggregate particles, in a similar way to the development of a microbial layer in Coupe et al.’s study. Biodegradation is a slow process, dependent on the type of contamination, but also the availability of nutrients. The authors suggest that the addition of a slow-release fertiliser (in this case struvite) could enhance the biodegradation process in the filter drains. In laboratory-based experiments, oil and street dust contaminants were added to filter drain models which were then monitored for a variety of properties in the effluent water including bacterial and fungal growth, heavy metals, pH, etc. It was found that biodegradation rates were improved by the addition of the fertiliser which was recommended for use in other drainage devices.
Coupe et al. and Theophilus et al. utilised small-scale models to replicate the environment in which they were able to test efficiencies at the microbial scale. At the other end of the scale, Lavers and Charlesworth’s study of Natural Flood Management (NFM) was applied at the catchment scale, or Catchment Based Approach, in this case, the rural Warwickshire Avon. By Working with Natural Processes (WwNP), engaging with local communities, farmers and land owners and careful design, the installation of NFM measures to slow the flow have the potential to provide flood resilience to downstream communities, as well as reduce pollution due to excess nutrients reaching local streams. Lavers and Charlesworth explain the methodology used to identify locations for these structures high up in the catchment including debris dams, off-line ponds and wet forests. They discuss the benefits of this approach as well as its limitations, the key lessons learnt during the study, and the potential application of this approach across different landscapes and land uses.
Responsible editor: Philippe Garrigues
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Charlesworth, S., Adeyeye, K. Special issue: developments in water management technologies and systems. Environ Sci Pollut Res 25, 19197–19199 (2018). https://doi.org/10.1007/s11356-018-1579-0