In most cases, solutions are applicable to all types of development and both new projects and refurbishments. However, some solutions such as rainwater harvesting or certain sustainable drainage techniques are only applicable to particular types of location or development.
Rainwater harvesting for example, is more suitable to buildings that have a large roof area or a concentrated water demand. WRAP very recently launched Rippleffect, a free water efficiency initiative that can benefit businesses of all sizes.
A design team can use a water efficiency plan to structure their efforts to reduce water use.
The plan could either be developed as part of the design process for new build projects, or initiated as part of a facilities management contract for an existing building. The plan should address the selection of fittings and appliances, user behaviour and should include for reductions in both potable water and hot water supply and use.
Minimising water consumption
There are various calculators available to predict water use at the design stage. When undertaking a Code for Sustainable Homes or BREEAM assessment, the BRE’s own tools should be used. These are the Code Water Calculator for homes and the BREEAM Wat1 Water Consumption calculator.
WRAP have developed a prototype spreadsheet based tool. The tool uses the same water consumption parameters as the BRE’s calculators. Where WRAP’s tool goes further is by demonstrating how design teams and facilities management contractors can quantify the savings from investing in water-efficient fittings and appliances.
The installation of water efficient fittings and appliances can also receive credits in both the Code for Sustainable Homes and BREEAM. Credits are awarded where the following measures are in place:
- Overall water efficiency better than Part G standards.
- Water metering technologies.
- Leak detection systems.
- Water butts for homes.
- Surface water management (i.e. SUDS).
The table below provides an example of the cost saving benefits that can be secured by minimising mains water consumption through taking an integrated water management approach in new build or refurbishment projects:
|Solution||Cost/Unit||Typical Savings (%)||Savings* (Litres)|
|Low flow taps
||60% compared to regular taps
||33 per person per day (based on 30% of water use for taps)
|Urinals with flow control
||50% compared with regular flush urinals
||5 per bowl per hour
||10 per bowl per hour
|Dual/low flush toilets
||3-6 per flush
|Low flow showers
||50% compared to regular showers
||30 per use
||30% of household water use
||55 per person per day
||30% of household water use
||55 per person per day
Key * Based on Hertfordshire average consumption rate of 182 litres per person per day (66.43m3/year) ** Variation in cost dependant on nature of harvesting product, 0 = no additional cost £ = low cost ££ = medium cost £££ = relatively high cost .
Read further information on different technologies and solutions (appliance, landscaping and irrigation, taps, toilets, urinals and water saving showers.
Using and reusing alternative sources of water
Using and reusing alternative sources of water, across all development types and scales, not only presents opportunities for reducing the demand upon mains water but also for reducing the amount of energy, carbon and chemicals that are used and emitted in the treatment and transportation of mains water.
Rainwater harvesting is the collection of rainwater that would otherwise have flowed into the drainage system or ground, or been lost to the atmosphere through evaporation.
Large surfaces such as roofs are ideal for rainwater harvesting. The most simple example of rainwater harvesting is a domestic garden rainwater collection butt. To maximise the amount of water collected, water butts should be fitted to a drainpipe. Pumps are available to enable the use of hoses with trigger sprays.
Another typical solution is the diversion of rainwater from the roof via a drainpipe into a storage tank (usually underground). Leaves and debris are filtered out before the water is stored. The filtered water cannot be used for drinking, but can supply toilets, outside taps, washing machines, etc. through a separate pipe network.
A control unit monitors the water level in the tank. If levels are low, the system switches to the mains water supply and if levels are high, an overflow trap allows floating material to be skimmed off and water to flow to a storm drain.
At a household level, payback periods for the more complex systems (i.e. use of rainwater to flush toilets, etc.) are long, typically more than fifteen years. However, larger projects such as schools and offices have a shorter payback time, often less than 5 years.
Greywater is wastewater from baths, showers and washbasins which can be collected, cleaned and reused for non potable uses such as toilet flushing. As it only relies on wastewater, greywater systems are not subject to weather variations.
Greywater usually only requires basic disinfectant or microbiological treatment to be reused to flush toilets. Problems can arise however, when the warm, nutrient-rich greywater is stored, as this presents an ideal environment for bacteria to grow.
Greywater systems are isolated from the mains water to prevent any contamination that could arise from backflow (complying with the Water Supply Water Fittings Regulations 1999). Greywater from baths and showers can be used safely on most non-edible plants, provided it is applied to the soil rather than foliage and is not hot.
At a household scale, greywater reuse can generate around 30% water savings. However, payback periods are not favourable and the maintenance burden can be significant. However, in other building types, particularly those where significant volumes of greywater (e.g. showers) are generated, payback periods are much shorter.
Greywater can be used for water reuse systems as long as suitable treatment is applied. Treatment systems that could be used include membrane technology, Submerged Aerated Filtration (SAF), biological treatment and Ultra Violet Light. Untreated wastewater should not be stored for long periods as it will naturally degrade and may create odours.
The Environment Agency’s 2010 report, ‘Energy and carbon implications of rainwater harvesting and greywater recycling’, emphasised just how important it is to specify the right system for each particular set of circumstances. Otherwise, the additional energy requirement introduced by a water recycling system can be greater than the environmental benefits of avoiding the use of potable water.
Blackwater is waste water that is highly contaminated, e.g. water from toilets and kitchen sinks. Blackwater should not be used for domestic reuse systems. Blackwater recycling systems use traditional biological methods as well as newer membrane filtration technology. In addition to holding tanks, often the systems have an attractive water feature planted with reeds, sedges or willows. These plants thrive on and clean up the nutrient rich water.
The treated water is clear, free of odour and contains little organic matter, allowing it to be stored and requiring little disinfection. The water can be reused for non-potable uses, or can be linked to a wider sustainable drainage network or local water feature.
Blackwater systems are expensive and typically have long payback periods. They are more affordable when the properties are distant from or have a small connection to the conventional sewage network. The integration of reed bed filtration within the landscape can also be aesthetically rewarding. The space (e.g. pond) requirements for blackwater recycling can be significant; a small cluster of five homes could need up to 200m2 of pond space.
Landscaping and irrigation
Watering of gardens and landscaped areas accounts for 5.6% of total water use in Hertfordshire and in summer can amount to up to 50% of total water use. Water-efficient gardening could significantly reduce the pressures on Hertfordshire's water supply.
Measures and techniques
The techniques and approaches suggested below can be instigated in a new area of landscaping or in existing gardens.
- Use healthy soil with plenty of organic matter to retain moisture.
- Choose plants for drought tolerance, compatibility with the soil and planting position.
- Plant new shrubs and trees through plastic to retain moisture, loose mulches can be used around established plants.
- Low-maintenance alternatives to planted areas include gravel and decking.
- Let the grass grow longer in lawns, this reduces the need for watering.
- Water in the early morning or late evening to prevent water loss from evaporation.
- A Mediterranean-style garden needs far less water to maintain. The plants suitable for such a garden are used to hot and dry conditions and are adapted to poor, free-draining soils.
- Drip irrigation can save water in large planting schemes. Porous hoses irrigate by "weeping" water on to or below the ground surface. Technically, these are unattended watering devices and therefore need to be on a metered water supply.
Managing surface water drainage
Sustainable urban drainage systems (SUDS) mimic natural drainage from a site and enable rainwater to run back into natural systems, rather than the stormwater drainage network. SUDS also treat run-off water to remove pollutants.
The SUDS water management hierarchy is:
- Prevention – using good site design and housekeeping measures to prevent run-off and pollution (e.g. minimise impermeable paved areas).
- Source control – controlling run-off at or very near its source (e.g. rainwater harvesting, permeable paving, green roofs or soakaways).
- Site control – attenuate and/or treatment of surface water for a group of buildings on site or a commercial park or a stretch of highway. The principle SUDS devices for a site control may involve a combination of devices including: detention ponds, swales, soakaway and infiltration trenches and basins.
- Regional control – attenuate and/or treatment of surface water for a region, serving a number of sites. Retention ponds and wetlands are the major regional treatment facilities.
There are a number of sustainable drainage techniques. Choosing which solution(s) to pursue depends on the attributes of the site and project, including:
- Local hydrology and hydrogeology.
- Ground contamination.
- Depth of water table.
- Soil permeability.
- Ground stability.
- Size of catchment area.
- Development type.
Natural on-site retention
Natural onsite retention includes drainage techniques that use natural features to infiltrate water, such as filter strips, swales, detention basins and balancing ponds.
Swales and filter strips
Swales and filter strips are vegetated surface features that drain water evenly off impermeable areas (e.g. roads). Swales are long shallow channels while filter strips are gently sloping areas of vegetated land on which runoff is directed.
Both solutions mimic natural drainage patterns by allowing rainwater to run through vegetation, slowing and filtering the flow. Swales work by attenuating and slowing down water flow to allow sedimentation and infiltration of pollutants. Filter strips only attenuate the flow slightly but they can be used to reduce the drained impermeable area.
Basins and ponds
An infiltration basin is a vegetated depression, which is normally dry except after storm events. Infiltration basins are built to store water temporarily to attenuate flows. They can also allow infiltration of water to the ground.
A balancing pond attenuates flows by storing run-off during the peak flow and releasing it at a controlled rate during and after the peak flow has passed. The pond always contains water.
Basins and ponds can be designed to control flow rates by storing floodwater and releasing it slowly once the risk of flooding has passed (a balancing pond). Basins and ponds should be designed to function in both dry and wet weather.
Basins and ponds treat run-off in many ways:
- Microbial activities
- Sorption and uptake by plants
- Absorption by soil
- Settlement of solids - plants in the water can promote settlement
- adsorption by aquatic vegetation/soil
- Biological activity
Engineered on-site retention
Common engineered solutions for onsite retention are soakaways, infiltration basins and filter drains.
- Infiltration devices allow surface water to soak and percolate into the soil, thereby re-charging the ground water and maintaining the water levels in local waters.
- Ground water and soil type can limit the infiltration systems, especially in high groundwater and clay soil areas. The base of an infiltration system should have sufficient unsaturated soil immediately below it to allow filtering of stormwater. The soils around the base and sides of an infiltration system should not be compacted which would reduce permeability or the infilteration efficiency of the system.
Cross-section through a traditional soakaway
Cross-section through an infiltration basin
Infiltration devices treat run-off in different ways:
- Physical filtration to remove solids.
- Sorption of pollutants by soils in infiltration devices.
- Biochemical treatment using micro-organisms.
Infiltration systems are easy to integrate into a site. They are ideal for use as playing fields, recreational areas or public open space. Infiltration systems can be planted with shrubs and other plants, which improves their appearance and provides a wildlife habitat. Infiltration systems also increase soil moisture content and help to recharge groundwater, which can mitigate problems of low river flows.
Pervious surfaces are key techniques in SUDS for surface water management and source control of he quantity and quality of runoff. Surface water is infiltrated through the surface and into the underlying construction layers where water is stored prior to infiltration to the ground, reuse or being released to the watercourse or other surface water drainage system. Pervious surfaces are often used for pavement, walk paths, driveways, car parks, cycle routes and sports ground.
Permeable pavement used for infiltration
Pervious surfaces can be either porous or permeable involving the following materials and techniques:
- Porous surfacing infiltrates water across the entire surface of the material forming the paving/car parking areas; e.g. grass and gravel surfaces, porous asphalt and porous concrete.
- Permeable surfacing consists of impervious material to water, however, voids are built-in to these materials that allow infiltration of water through the minute void channels; e.g. concrete paving blocks.
They are effective to provide attenuation of water flow treatment. Pervious paving would ameliorate the need for surface water drains, allowing runoffs to permeate through porous pavements, such as permeable concrete surfaces, crushed stones or porous asphalts. Pollutants removal by filtration occurred within the surfacing or sub-base material itself, or by the filtering action of the reservoir or sub-soil. Some biological breakdown of organic pollutants can also occur.
Permeable surfaces can be designed to fit in with a variety of environmental settings, e.g. hard surfaces of a car park, town centre or gravel surfaces for light traffic. They can be grass-crete or soft landscape surfaces for rural areas. Infiltration devices can be incorporated into open space areas, e.g. playing field or car parks as part of a flood management scheme.
Minimising wastage in water distribution: leak detection
Minimsing the wastage of water through the mains water distribution network can provide significant reductions in water consumption to the building occupants or residents therefore reducing the demand upon the water treatment and supply infrastructure and our water resources. The key to achieving this lies in leak detection.
Leak detection devices are used mainly to prevent damage from pipe bursts in unoccupied buildings, with water saving as an added benefit. Many products are designed to detect pipe bursts and leaks and shut off the water supply to minimise water loss and damage. Most provide a simple switch to turn off the water when the building is unoccupied for any length of time.