As a result of climate change, longer and drier summers are expected in the long run, while rainfalls are expected to decrease. Water requirements have been dramatically increasing in modern cities for the past decades. This horizon has raised the concerns because water is not a non-exhaustible good. In addition, pollution is a constant threat to the quality of groundwater, watercourses, and rivers. Experts are concerned about the unclear future of this precious resource, and it has become evident the need to use alternative, more sustainable water sources as well as using all resources in a more efficient way in developments to be able to provide for all water requirements, from households to farming, and indirectly even natural habitats.

2.10.1 Sustainable water sources

• Rainwater harvesting: it is advisable to design and install water collection systems for reuse in both new and old buildings. Such systems go from water butts for gardening to more sophisticated systems that can supply water for different domestic uses, like personal washing, laundry, and toilet flushing. The storage tank can be placed on the roof or underground. Besides down pipes connecting to the tank, separate pipes are necessary to carry greywater or rainwater. In addition, there should be a mains water and a mains supply back up.

Fig. 1. Water butts. Source: “SmartDesign-Creating Sustainable Buildings”

• Greywater recycling: Systems to collect, cleanse, and re-use greywater can be installed and used in single housings as well as in developments. Greywater from baths, showers, and hand basins is generally suitable for flushing the toilet, although it is advised to use disinfectant or microbiological treatment. To keep biological activity from occurring, greywater should be filtered before being stored for its later use.
  
  “Greywater is wastewater generated by household processes such as washing dishes, laundry and bathing. Greywater is distinct from wastewater that has been contaminated with sewage, which is known as blackwater”
  (www.wikipedia.org/wiki/Grey_water)
  
• Integration of domestic water systems: Integrating water conservation measurements can lead to important savings in water consumption.

Fig. 2. Water use within the home.
Source “SmartDesign-Creating Sustainable Buildings”

Fig. 3. Combined rainwater/ Greywater system.
Source: “SmartDesign-Creating Sustainable Buildings”

2.10.2 Efficient use of all water resources
It is necessary to reduce the demand of water and to find alternative sources to lower the use of expensively treated drinking water in uses such as flushing toilets. Industry leads the consumption of water. It is followed by hospitals, hotels, schools, and residential developments. However, there are different and very simple ways to reduce this consumption up to 50%:

• Installing low water use appliances (i.e. low water use washing machines and dishwashers)
  
• Installing water efficient fixtures, like low/dual flushing toilet systems (these systems use 4 litres per flush instead of the 9 litres/flush of clean drinkable water in traditional toilets), waterless urinals and toilets, and aerating heads (These can save up to 80% of water used in regular taps).
  
• Water meters can help increase awareness of water consumption
  
• Designing landscape sustainably. The aim is to achieve low water consumption as well as a low maintenance. In order to accomplish that, the landscapes designs should include indigenous plants and drought tolerant species, which also a have a better chance for survival with the expected warmer climate patterns.
  
• Avoid power showers. Savings of up to a third of a a bath’s water can be achieved in quick showers. However, power showers can consume more water than a bath in less than five minutes.
  
• Re-use water collected in air conditioning systems as well as in swimming pools applying the proper treatment.
  

2.10.3 Sustainable Urban Drainage Systems (SUDs)
Traditional drainage systems can cause flooding by allowing water to rapidly move from where it falls to a point of discharge, for instance a watercourse. In addition, they can affect water quality because of the pollutant agents contained in the run off, and also groundwater is affected if there is little natural infiltration. Even drainage systems related to new developments may affect biodiversity.

Sustainable Urban Drainage Systems (SUDs) are structures designed to receive water run off and provide drainage similar to natural processes instead of piped solutions.

SUDs are more efficient handling polluted water since they receive rain close to its source, and they are capable of slowing down flows across sites and into watercourses. This allows settlement, filtering, and infiltration. SUDs also help reduce pollution in water streams. Some SUDs techniques are:

• Soakways: vegetated areas with a slight slope that allows draining water off impermeable areas. They also filter particles such as silt. They can be an alternative connection to the piped system.
  
• Permeable surfacing: surface water trespasses porous materials, such as concrete, blocks, crushed stone/gravel, or porous asphalts and penetrates the ground. Depending on the type of soil, water may infiltrate directly into the subsoil or remain in an underground reservoir, before slowly drenching into the ground. If necessary, to keep the pavement free of water at all times, it is possible to use an overflow. Pollutants are removed either within the surfacing material itself or by filtering of the reservoir or subsoil.
  
• Swales and basins: swales are dry channels or ditches, and basins are dry ponds. Both store storm water temporarily, reduce peak flows to receiving waters, and enable the filtration of pollutants and microbial decomposition. They also facilitate water infiltration directly into the ground. They can be ornamental or be integrated as part of the landscape. They are usually a part of drainage network connecting to a pond or wetland before discharging to a natural watercourse. They can replace kerbs alongside roads, saving construction and maintenance costs.

Fig. 4. Example of a swale in use at a housing estate in Dundee.
Source: “SmartDesign-Creating Sustainable Buildings”

• Infiltration trenches and filter drains: they are stone filled reservoirs that receive stormwater runoff, and through them, water slowly infiltrates into the ground. To remove excess solids, filter strips, gullies or sump pits can be introduced at inflow points. The difference with filter drains is that these ones have a pipe running through them. They are highly used in draining roads and help slow down runoff water. They allow storing and filtrating water before reaching the discharge point. Pollutants are absorbed, filtered and even decomposed by microbial action in the soil.
  
• Ponds and wetlands: during heavy rain they are capable of holding important amounts of water, reducing flood risks. They are recommended in large sites, and they can be integrated as part of the landscape. They are also very efficient removing grits. Filtering is enhanced by the action of algae. Ponds and wetlands can be fed by swales, filter drains, or piped systems.
  
• On site Stormwater Detention (OSD): they replace SUDs where they cannot be used because of the soil and ground features. They are based on the installation of large diameter pipes, culverts or tanks. A storage tank receives surface water runoff from roofs, car parks, and large paved areas. After being stored, water is discharged to a main sewer. When heavy rain is over, the storage tank is usually emptied, getting ready for future storms. This water can also be used in gardening or in fountains, and mechanical misters for evaporative cooling.
  
• Reed bed filtration: it is a sewage treatment system. It improves the cleanliness of septic tank discharges. They are planted in gravel supply, and they provide oxygen to bacteria in the gravel. These bacteria clean up the sewage, and the water discharged to a watercourse after acting upon it, is clean and harmless to the environment and wildlife. This system is the most suitable in rural areas because of its lowest cost. They also help the development of a habitat for insect and amphibians.

2.10.4 Green roofs
This type or roofs are vegetated to a large extent, and they can retain up to 90% of rainfall. Rainwater flow rate is slowed down, and flooding is reduced. Green roofs can go from fullblown roof gardens to grassy swards and sedum roofs. In addition, they not only contribute to hygrothermal comfort, but they have many beneficial effects on the environment since they are capable of retaining dust and polluting substances in the vegetal layer, they are very efficient protecting from solar radiation, they increase the cooling capacity of the building because of the evaporation process (with the subsequent improvement on the surrounding environmental humidity), they improve insulation and the interior thermal stability, and they are good sound absorbents.

2.10.5 Xerogardening
Xerogardening is the type of gardening based on using plants with low water requirements that best fit the climatology of the area, after a previous and careful analysis of the ground to determine the physical, chemical, and topographical characteristics of the garden, as well as and exhaustive study on the weather or the microclimate of the surroundings. The design of the garden will depend upon these two studies, comprehending not only the type of vegetation, but also the irrigation system. This garden also includes a protective layer for the soil, called “mulching” made of vegetal resources which prevent from evaporation that contributes to erosion and superficial run-off of the ground. Maintenance is constantly performed on the garden.

This type of gardening is widely advisable not only in individual housings, but also in public parks, as a means for water saving.

Fig 5. Green roof constructive detail and photo

Further Information:
Environment Agency, www.environment-agency.gov.uk
Construction Industry Research and Information Associated (CIRIA), www.ciria.org.uk
Thames Water, www.thames-water.com

Regarding irrigation, the most efficient systems are based on sprinkling rather than flooding since the amount of water can be regulated by a set of mobile devices attached to a secondary water distribution net from a well or a subterranean container. Water is distributed by gravity or pumping. However, this system has several disadvantages if compared to dripping or microirrigation since it requires higher water consumption and the distances between sprinklers has to be constant in the 80% of the surface.

Microirrigation or dripping provides water in a more constant way and in little amounts to the roots, keeping humidity stable. Since water is provided subterraneanly, losses because of evaporation are avoided, maximising the use of water. This system is made of small diameter pipes with valves beside each irrigation point, connected with an emissor or dripper. These emisors can be controlled electronically.

Fig. 6. Dripping Systems.
Source: www.c-sostenible.cat

If water is too hard, it is possible to reduce its lime content by using water conditioning systems for water irrigation, therefore, preventing pipes obstruction and calcification.

Fig. 7. Drippers

References

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