Approved Document G and the Water Calculator

In this exclusive extract from NBS Shortcuts, written by noted industry figure Austin Williams, we introduce the increased requirement for water efficiency.

The Millennium Development Goals, set at the United Nations' Millennium Summit in 2000, agreed to reduce by half, the proportion of people without access to safe drinking water by 2015, which is the closing year of the International Decade for Action: 'Water for Life'.

As part of its commitment, the UK government is emphasizing the need for a paradigm shift in the way that we see water use. Now, saving water - or promoting water efficiency - needs to figure more highly in designers' considerations. Using a lot of water used to be seen as a mark of civilization; now, it seems, less is more.

The updated version of the Building Regulations (England and Wales) Approved Document G Sanitation, hot water safety and water efficiency says that, not only should water be used less profligately than it is at present, but that designers should provide evidence to that effect.

The new AD G applies to the erection, extension and material alteration of a building, not just dwellings. In fact, it applies to all new buildings - and building designs except where work has commenced or a plans certificate has been given prior to the date that the new AD G comes into force.

Even though the word no longer appears in the title, 'hygiene' is a very important feature of the new AD G . A sink will be required wherever food is prepared, for example, a recommendation not previously thought necessary until the recent spate of bacteria fears.

But it is the performance targets that are what the amendments are all about. Compared to the contemporary average of 149 litres of water used in the UK per person per day, AD G sets a target of at least 125 litres per person per day. Commentators have suggested that minimising water consumption by 25 litres or so should not be too onerous.

This target 125 litres includes 5 litres per person per day for outdoor use - watering the garden, say - so dwellings with no gardens may consider omitting the external use quota and working to 120 litres per person per day. A basic compliance with AD G's 120 litres per person per day equates to the Code for Sustainable Homes Code Level 1 for internal water use. To attain Code Level 6 - the highest sustainability rating - a domestic property must use no more than 80 litres per person per day. Bear in mind that Africa's average for water use is 68 litres per person per day.

Water Calculator

The 'Water efficiency calculator for new dwellings' (known as the 'Water Calculator' for short) must be used to assess the notional water consumption of the dwelling. Each water-using fixture or fitting has to be assessed in turn and its capacity in litres or its flow rate in litres per second - taken from manufacturers' data - entered into a table.

Multiplying by a use factor results in the amount used per person per day. For example, on average, the Water Calculator tells us that we full-flush a dual flush toilet 1.46 times per day!

A simple sum provides a figure for the water use for each appliance. These are added together to give the total water consumption of the home, and divided by the number of occupants to give the per person daily rate.

Finally, any recycled or harvested water is discounted from the total and the external water use factor of 5 litres per day per person is added (provided that the property includes an external environment that requires water) to give the full and final total water consumption rates.

Please note that non-fixed, reduced-flow devices such as toilet Hippos, should not be included in the equation, as future occupants could easily remove them and distort the water use rating results.

Find out more

The full text of this NBS Shortcut is exclusively available as part of NBS Building Regulations.

NBS Shortcuts is a new series of illustrated "how-to" articles and guides, covering a wide range of practice, regulatory and design guidance. The easy to follow text and detailed hand-drawn graphics will aid any building designer. They are available online as part of your subscription to NBS Building Regulations.

Related NBS information:

Selected links:

• Part H: Drainage and waste disposal
• Video: The Anticipated New Approved Document G and the Water Efficiency Calculator

Selected links:

• Bathroom fittings/furniture/equipment
• Drainage, sewerage

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