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February 21st 2016
6 min read

New Water Efficiency Regulations

Demand for water is already increasing year by year due to population growth, but over the next 2 decades this is likely to rise substantially due to an ambitious programme of development and increasing per capita water consumption. Unfortunately, there is likely to be less water available because of climate change and tighter controls on water extraction. By and large, the picture is of an escalating demand for a limited resource - less water will need to go further!

Government Regulations – Part G of the Building Regulations and the Code for Sustainable Homes

The Government is pushing a feasible development programme that orders improved water efficiency in the building industry. The Code for Sustainable Homes was introduced in 2007 and Part G of the Building Regulations now includes water efficiency for the first time.

Under the new Part G of the Building Regulations, anyone building a new house will need to comply with the new water efficiency regulations and therefore, will have to calculate how much water they will be using.

  • Building Control will now require you to provide calculations demonstrating that your proposed dwelling can function at a level of water consumption of less than 125 litres of water per person per day.
  • This calculation also takes into account the use of grey water systems.
  • It is now a requirement within the Standard Assessment Procedure (SAP)calculations that all dwelling units should have a Water Efficiency Calculation carried out. In order to comply with these regulations designers and developers will now have to give particular thought to the choice of sanitary ware, plumbing fittings and white goods to be installed in the dwelling. To calculate the combined water usage of a property, flow rates of plumbing fittings, including taps and shower valves, along with bath sizes, toilet cistern flushing volumes and water usage by dishwashers and washing machines etc. will all need to taken into account.

Online calculators such as are available to assist developers create water efficient buildings.

These regulations are a little daunting at first, but the following list of Questions & Answers may help to simplify things for you:

Question: What water efficiency targets now have to be met?

Answer: Regulation 17K introduces a minimum water efficiency standard into the Building Regulations for new homes (including those created by a change of use). It requires that the average design water usage of a new home is no more than 125 litres per person per day.

Question: How do I calculate the average design water usage of a new home?

Answer: The estimated water usage must be calculated in accordance with the published methodology set out in the “The Water Efficiency Calculator for New Dwellings”. This is available at:

This methodology is exactly the same for calculating water use for both Part G of the Building Regulations and the Code for Sustainable Homes.

Question: When do I actually have to complete the Water Calculator?

Answer: Regulation 17k requires only that a notice is given to the building control body within five days of the completion of work*. The notice needs to state the potential consumption. However, in practice, a copy of the completed calculation table should be submitted to the building control body. * Where the building control body is an approved inspector, not later than the date on which the initial notice ceases to be in force under regulation 18 of the Building (Approved Inspectors etc) Regulations 2000 if that is earlier. To ensure the fittings and appliances are specified during the design stage, the Water Calculator should be completed initially and then revised if those fittings subsequently change

Question: I have calculated the water usage of a new home for the Code for Sustainable Homes, do I have to repeat this calculation for Part G.

Answer: No, the methodology is the same for both. Any home meeting Code Level 1/2 will also meet Regulation 17K of the Building Regulations.

Question: Can I create my own spreadsheet to do the calculations?

Answer: Yes you can, but you would need to ensure that all the calculations are correct and these calculations would have to be verified by the Building Control Body so it would probably be better to use one of the online water calculators which have been verified by LABC and the Building Control Alliance.

Question: Where can I find information on fittings in order to complete the water efficiency calculation?

Answer: Information can be found from manufacturers. The calculation should be based upon the data for the fittings actually installed.

Question: How do I save a copy of the calculation?

Answer: Once you have completed your calculation, print the document to pdf. and then send it with your building notice to the building control body.

Question: If I have a bath shower mixer tap do I count it as a bath or a shower?

Answer: You need to complete the bath calculation using the ‘bath’ tab in the electronic calculation. You also need to include the mixer tap as one of your showers using the ‘shower’ tab in the electronic calculation.

Question: How do I carry out the rainwater harvesting calculation?

Answer: First complete the calculations for the water using products (e.g. taps, toilets). Using the published method, enter data for your selected Rainwater Harvesting System into Table 5.1. Use the calculation from Table 5.1 to complete Table 5.2. This gives you a value for “Rainwater Collected (a)” in the electronic calculation. Then either:

  • If all toilets are to be supplied by rainwater, use the WC water usage (total litres/person/day for all types of toilets) from the 'water calculator' tab in the electronic calculation to provide a value for “Rainwater demand (b)”; and
  • If all washing machines are to be supplied by rainwater, add the washing water usage (total litres/person/day for washing machine) from the 'water calculator' tab to the WC water usage to provide a value for “Rainwater demand (b)”. Or
  • If not all toilets and/or washing machines are to be supplied by rainwater, use Tables 5.3 to 5.5 of the published methodology to give you a value for (b). The value (c) will be calculated automatically. There is no need to press the 'calculate' button.

At Easy Bathrooms we have a number of products that comply with the water efficiency regulations

  1. The LEIGHLIBRA BATH (1700 X 700 in super strong acrylic (8-10mm thick) ~OPTION TO LOWER OVERFLOW ~


  1. When choosing a toilet, a good option would be the ALFRICK CLOSE COUPLED TOILET which features an eco-friendly dual flush system, providing a choice of 4.5 litre and 3 litre flushes.

The fully trained advisors at Easy Bathrooms are always ready to offer advice and assistance, so why not call into one of our showrooms now and take advantage of the 30% off discount available on all the products listed in this article. (Limited period only)

*a flow restrictor is placed on the water feed and aerator