Last edited 23 Apr 2019

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Buro Happold Engineer Website

Water consumption


[edit] Introduction

Water is a critical and finite resource. It covers over 71% of the Earth's surface and is essential for life, playing a key role in the production of food, human health and sustaining the natural environment.

However, water, particularly of drinking water quality, is becoming increasingly scarce in most of the populated regions of the planet. The pressure is on to reduce water demand by reducing wastage, to reuse or recycle as much as possible, and to look at other means of minimising our impact on the water environment. Overall, we must be more efficient with our water utilisation.

This notion that it is important to conserve water is not a recent one. Whether it is the intricate reservoir and sewage systems of the Indus or the more aqueduct systems found in imperial Rome, the need to use water efficiently has been innate in human populations since the birth of modern civilisations. However, we now need to find new ways to conserve water and to use it efficiently.

[edit] The national and international context

In 2006, the House of Commons Science and Technology Committee on water management suggested that, 'Water resources in England and Wales are threatened by below average rainfall in the short-term and climate change in the longer-term. The use of these resources is also facing increasingly tight regulation in order to meet ever higher ecological requirements. Simultaneously, demand for water is increasing because of population growth, a decreasing average household size and growing use of water-intensive appliances'.

In 2012, the global population was estimated at 7,060,253,019 (USCB, 2012) and is expected to rise to over 9 billion by the year 2050 (GeoHive, 2012). This rise in population is one of the main reasons for the pressure on water resources. The areas that will experience the highest rates of population growth are in developing countries where water is in short supply due to factors such as drought and poor water conservation.

At the Waterwise annual conference in 2009, Pamela Taylor said, “In the end, avoiding waste – of water or anything else – is a society thing. Companies can supply; regulators can tell them how; NGOs can organise campaigns; governments can set policy. But unless there's a collaborative effort to explain why it matters, then it's very unlikely to succeed.”

The water that we use in the United Kingdom is pumped, purified, treated and heated before it reaches our homes. This process greatly increases the amount of energy that we use. Domestic hot water usage alone is responsible for 35 million tonnes of greenhouse gas emissions (DEFRA). When we are wasting water, we are also wasting the energy that is used in preparing it for use.

Global water stress.jpg

Technically, there is enough freshwater on Earth to fulfil the needs of the global population, but a combination of factors mean that there are significant scarcity issues in many areas:

  • Demand distribution does not match resource distribution. Population densities are becoming more localised, consumption patterns are changing, and new demands are emerging (for example, bio-fuels could become a significant water user of the future). This all stresses the resource at a local and regional level.
  • Social access. In many places there is sufficient water, but people cannot access it due to asymmetric power relations, poverty and related inequalities.

Climate change is accelerating global water circulation, amplifying climate variability and temporal water scarcity.

[edit] Part G of the Building Regulations

Part G of the UK building regulations (Sanitation, Hot Water Safety and Water Efficiency) sets out requirements for washing facilities, bathrooms and hot water services. As the need to conserve water has become more important, so part G has become a more extensive document.

Part G focuses on six main aspects of water conservation:

There are also a number of amendments to the 2009 edition. These include composting toilet arrangements, rainwater and greywater, and water efficiency.

According to amendment 17k of part G, The maximum allowable consumption of potable water in new dwellings is 125 litres per person per day. As reported by recent studies (ref. Environment Agency, 2012) the water consumption of the average person in the UK is 150 litres per day. This means that the regulation dictates a decrease in the daily water consumption by at least 25 litres.

[edit] Project approach

The various building rating schemes all reflect the heirarchical approach of reducing demand for water at source, ensuring efficient distribution (including metering, leakage detection etc), and then use of alternative sources.

Reducing water demand.jpg

[edit] Reduce demand at source - efficiency

Water use.jpg

There are a number of relatively straight-forward water efficiency measures that can be made that not only conserve water but also save money. Water efficiency should be specified on all projects, unless it can be proven to be to the detriment of other systems.

All fittings in the UK should comply with the Water Supply (Water Fittings) Regulations 1999. There may be financial benefits if technologies are on the Water Technology List and qualify under the Enhanced Capital Allowance Scheme (this offsets the cost of the technologies against tax for that year).

A brief overview of the potential savings are outlined below:

Water efficient devices.jpg

Baseline water consumption can be reduced at source through passive or active measures.

[edit] Passive measures

Passive measures are those which require no behaviour change by the user. They include:

[edit] Handbasins

  • Water Saving Taps (efficient versions are as low as 1.7 L/min) are often the same price as less efficient models.
  • Appropriate sink sizing. If a sink does not need to be completely filled to use it, then a smaller sink could be specified.
  • Foam soap requires little water to remove, and generally means less soap and water are used.

[edit] Low flow toilets

  • Toilets are typically the largest water user in non-residential developments, allowing significant savings to be made.
  • Modern standard cisterns have a volume of 6L. Efficient designs can bring the average flush volume down to 3L.
  • Siphon mechanism. Low flush (4.5L) versions are available, but they are slow to refill the cistern and are only available in single flush.
  • Drop valve mechanism. Allows quick cistern refill (good for high frequency use) but the valve will eventually leak, and it is not as robust as the siphon. It may also require maintenance to remove scale deposits.
  • Delayed action inlet valve. This prevents water flowing into the cistern before the flush is complete.
  • Interruptible flush. The user stops the flush by releasing the lever when the pan is clear.
  • Composting. A tank or chamber is installed below the toilet bowl to collect waste. Liquid waste can be collected separately, diluted and used as fertiliser for trees and flowers. The solid waste can be collected after 6months to a year and used as compost.
  • Vacuum. These use air rather than water to flush, and can be used where gravity drainage is problematic. Some designs combine an air and water flush.

[edit] Urinals

Urinals are often set to flush regardless of use, typically 3 times an hour. A number of devices can be used to control flush frequency:

  • Hydraulic valve. This can be fitted to the inlet pipework of the urinal system. When water is used elsewhere in the washroom, the pressure decreases temporarily, the valve opens, and allows a pre-set volume of water to pass into the cistern. When the cistern is full, an auto-siphon will discharge and flush the urinal.
  • Passive infrared (PIR) sensor. This can be installed in the washroom to detect use of the urinal system. The sensor controls a solenoid valve which allows a pre-set volume of water to pass into the cistern. When the cistern is full, an auto-siphon will discharge and flush the urinal. A PIR sensor can be battery operated. Out-of-hours it can be set to deliver a 'hygiene flush'.
  • Manual shut-off. If usage hours are predictable, a single valve can be installed in the pipework supplying the washroom. This can be closed manually each day.
  • A timer can be installed so that the water supply is shut off during periods of non-use. This is a more flexible and reliable alternative to manual shut-off.
  • Waterless urinals. Can work effectively with the correct maintenance regime. There are three main types:
  1. Siphonic Trap. These contain a barrier fluid which the urine passes through.
  2. Deodorising pad / biological cartridge are fitted to break down bio-film.
  3. Air-flush. Individual traps are replaced by a single trap at the drain end. A low wattage DC fan provides airflow down the bowl to prevent odour. There are no chemicals and they are easy to clean.

[edit] Water efficient appliances

The Environment Agency reports that dishwashers and washing machines account for over 16% of domestic water consumption. Typically, washing machines use less than 50 L/cycle, and dishwashers less than 15L/cycle. Efficient versions use much less (40L/cycle and 10L/cycle), and modern washing machines often have a 'half load' cycle or intelligent monitoring to only use as much water as needed.

[edit] Efficient distribution

  • Leak detection and water meters can help highlight excessive use, or unusual usage patterns.
  • All modern domestic pipework should be fitted with an isolator valve, with integral flow restrictor. However, should the water pressure fall, the flow may no longer be adequate. There may also be difficulties with blockages in hard-water areas due to scale buildup.
  • Water mains are usually operated at about 2-4bar, but in some cases higher pressures than necessary can be delivered to the lower floors of tall buildings. Over-high water pressure can result in excessive water consumption, cause or exacerbate leakage and put additional wear and tear on the distribution system. Pressure reducing valves (PRVs) can be used to control the pressure in the incoming main or distribution system (e.g. in the supply to each floor, the down service of a gravity-fed system, or the risers in a pumped system). They can be pre-set or adjustable, and accept delivery pressures of up to 25bar and deliver pressure of 1.5 to 6 bar under variable flow conditions.
  • Lag pipework to reduce heat loss/gain and so avoid the practice of running water to drain until it achieves the correct temperature.
  • A solenoid valve linked to a lighting control module via a PIR will shut off the water supply to the toilet area to prevent wastage due to leaks.

[edit] Alternative sources

Examples of alternative sources for water utilisation are rainwater harvesting, greywater reuse and blackwater reclamation.

[edit] Rainwater harvesting

In areas where there is insufficient surface water or where groundwater is particularly inaccessible but there is an abundance of rainwater, rainwater harvesting can be effective.

Despite the fact that the United Kingdom receives a high level of rainfall, water resources are under serious pressure. Rainwater harvesting systems range from the humble water butt used to water domestic gardens, to schemes such as the Millennium Dome in London in 2000, where rainwater was collected from the 100,000 sqm roof and filtered through reed beds in the landscape before being returned to the Dome and used to flush the 700 toilets. Typically, rainwater is collected from building roofs and then stored in a tank for non-potable use. Most non-potable water applications do not require UV or chemical treatment, although treatment might be appropriate depending on the potential for human exposure.

The Code for Sustainable Homes (2006) encourages the installation of rainwater harvesting systems in newly built homes for use in the garden, washing clothes and dishes and other domestic uses such as flushing toilets. It has been reported that this can reduce the amount of mains water being used by up to 50%. The Environment Agency suggests that, 'reducing the volume of mains water supplied means that less water is taken from lakes, rivers and aquifers and more is left to benefit ecosystems and help sustain the water environment'.

See Rainwater harvesting for more information

[edit] Grey water recycling

Greywater is wastewater from showers, baths, washbasins, washing machines and kitchen sinks. It is possible to collect such water and, after treatment, use it for purposes that do not require drinking water quality, such as toilet flushing and garden watering. (Environment Agency, 2011). This greatly reduces the demand on mains water as well as reducing the volume of water discharged into sewage systems.

As well as conserving water this will also save users money on their water bills (if they have water metres installed). According to the Environment Agency (2011), greywater recycling systems have the potential to reduce the amount of mains water used in the home by about a third.

The limitations of initiatives such as rainwater harvesting and greywater harvesting are that even though it reduces demand for mains water, it does not actually contribute to a reduction in water consumption. In addition, long payback times combined with small storage volumes mean it can be less effective than other water conservation measures.

[edit] Conclusion

There are many challenges in implementing sustainable water management practices. There is a social reluctance to change habits and routines, and it is a field laden with expectations and prescriptive legislation. This means that the physical systems which make up our current infrastructure have a high degree of inertia over time. Change will only happen slowly, alongside the development of knowledge, understanding and acceptance.

The safe implementation of water recycling and reuse in all countries and for all types of applications requires the development of a global framework including regulatory requirements and policies, water quality control and risk assessment, design and operational recommendations with codes of practice, as well as communication and education with stakeholder and community involvement. In the UK there is now a British Standard for rainwater recycling (BS8515:2009) and BS 8525 for greywater.

This article was originally created by Atehrani 11 March 2013.

It has been significantly developed and extended by --Buro Happold 23 July 2013

[edit] Related articles on Designing Buildings Wiki

[edit] External references

[edit] Bibliography


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