Who is the calculator aimed at?
The calculator is designed for anyone involved in the development of new homes, e.g. developers, Housing Associations and others. It is designed make it quicker and easier to comply with the water aspect of Building Regulations and/or the Code for Sustainable Homes.

Can I use the results from the calculator in a planning application?
Yes you can, provided you have the calculation results verified and approved by a Building Control Officer or suitably qualified Code for Sustainable Homes assessor.

Why should I want to use the calculator?
The calculator is designed to be used by anyone who is involved in the design and construction of new homes. It has been designed to be easy to use and results can be returned in 3 simple steps. Once you have your results you can print them, print with the product specified data or save them for later reference.

Can I save my results for later viewing?
Yes you can. You can save your results at the end of your calculation by clicking the save button. You will need to register with the calculator to do this, but don't worry, registration is just your email address and a password so you can retrieve your data later, there are no personal details required.

The product I want to use isn't in the list; can I enter my data/values manually?
Yes you can. Simply follow the instructions on the popup data input screen, clicking the small square on the right of the input boxes turns them to manual input, but remember to give your product a name so that when you print out your results you will know what you have specified.

What is Part G of the Building Regulations?
The Government updated Part G of the Building Regulations in April 2010. This sets a whole building standard of 125 litres per person per day for domestic buildings. This comprises internal water use of 120 litres per person per day, and in that respect is in line with Code Levels 1 and 2, plus an allowance of 5 litres per person per day for outdoor water use. This will be specified using the methodology set out in the 'Water Efficiency Calculator for New Dwellings' also used for the Code for Sustainable Homes.

What is the 'Water efficiency calculator for new dwellings'?
The 'Water efficiency calculator for new dwellings' is the Government's national calculation methodology for assessing water efficiency in new dwellings in support of The Code for Sustainable Homes and the Building Regulations. If you are building a new home you will need to use the methodology outlined in this document to calculate the water consumption of the dwelling. This is calculated using a number of assumptions outlined in the guidance and is calculated in litres per person per day. The water calculator provides an on-line up-to-date version of this, enabling you to comply with regulations quickly and easily.

What is the Code for Sustainable Homes?
Introduced in 2007, the Code for Sustainable Homes is the Government's main tool for improving the environmental specification of new homes. Points are awarded for achieving set standards in 9 different aspects of development. There are seven levels of specification ranging from level 0 (the Building Regulations) to level 6 (zero carbon). Water consumption inside the home is one of the compulsory aspects to address to achieve minimum standards at levels 1-6 of the Code. Daily PCC of water is calculated using the 'Water Efficiency Calculator for New Dwellings' as detailed in the Code for Sustainable Homes Technical Guidance. A total of 5 credits are available for water consumption.

The water consumption specification for increasing Code levels are:
Level 0 - Part G of the Building Regulations
Levels 1-2 - less than 120 litres/person/day
Levels 3-4 - less than 105 litres/person/day
Levels 5-6 - less than 80 litres/person/day

What does Part G of the Building Regulations mean for me?
If you are building a new home, you must ensure that it will have a predicted water consumption of less than 125 litres/person/day using the methodology outlined in the 'Water Efficiency Calculator for New Dwellings'. This site provides a working example of this and also contains information on water consumption for hundreds of products, enabling quick and easy specification, without the hassle of collating data from several product manufacturers. You can use our example specifications if you need a quick starting point.

Am I required to meet minimum Code for Sustainable Home requirements?
For the private sector, the Code is a voluntary initiative, although the Government does plan to tighten building regulations to reflect higher levels of the energy aspects of the Code between now and 2016.

Through the planning system, the Government has given local authorities the option of asking for higher than mandatory Code levels for both private and public funded homes in order to reflect local conditions and priorities. Your local authority may have a requirement for developments to meet minimum Code levels, and if so, this will be outlined in their Local Development Framework.

As a condition of financing housing associations, The Homes and Communities Agency requires that all new homes built with public money meet at least Code Level 3 from May 2008.
If you are building a new home to a specific Code level, you must ensure that it will have a predicted water consumption that is within the minimums required for that level of the Code using the methodology outlined in the 'Water Efficiency Calculator for New Dwellings'. This site provides a working example of this and also contains information on water consumption for hundreds of products, enabling quick and easy specification, without the hassle of collating data from several product manufacturers. You can use our example specifications if you need a quick starting point.

The Code for Sustainable Homes Technical Guidance and/or the Water Efficiency Calculator for new dwellings have been updated since I began my development, which version should I work with?
A new home aiming to meet any given Code level must meet the requirements of the Code at time it was registered with a Code Assessor. Should the Code be updated between the time of registration and the time of completion, the developer has the option of meeting the requirements of more recent versions of the Code. This site is kept up-to-date and should represent the most up-to-date version of the Water Efficiency Calculator for New Dwellings.

How do I calculate how much my greywater harvesting system will contribute to my development?
To calculate this, you will need to enter 3 values into the calculator, the water usage of the fittings supplying your greywater system, the percentage of water to be recycled and the greywater demand.

To calculate the water usage of the fittings supplying your greywater system you will need to add together the water consumption of the fittings that will supply your grey-water system e.g. shower, bath and taps excluding kitchen/utility rooms. To do this you can use the totals given in the water calculator in litres/person/day on the far right hand column.

The percentage of used water to be recycled should be available from the product manufacturer.

To calculate greywater demand you will need to add together the total water consumption of the fittings that will be supplied by your greywater system i.e. the toilet(s). If you have more than one toilet and your system does not supply all of them, you will need to ensure that you only add the correct proportion of water for that toilet.

Please note that if you are collecting greywater and rainwater, you must ensure that water demand is split equitably between the 2 calculations, so that there is no double-counting of water saved.

How do I calculate how much my rainwater harvesting system will contribute to my development?
Factors that will affect the volume of water harvested will include the average rainfall in the area, the size of the collection surface, the material used on the collection surface, the slope of the collection surface, the size of the collection tank and the efficiency of the filter. To calculate how much water this will supply per person, you also need to estimate the number of occupants (estimated at 2 people for the main bedroom and 1 person for all other bedrooms.) Our water calculator uses this information to make a simplified calculation of how much water your system will supply. The product manufacturer should be able to help you find this information.

To calculate rainwater demand you will need to add together the total water consumption of the fittings that will be supplied by your rainwater system i.e. the toilet(s) and/or washing machine. If you have more than one of these items and your system does not supply all of them, you will need to ensure that you only add the correct proportion of water for that item.

Please note that if you are collecting greywater and rainwater, you must ensure that water demand is split equitably between the 2 calculations, so that there is no double-counting of water saved.

The Water Calculator guidance provides further information on how to calculate rainwater harvesting contribution to water consumption.

I have used the calculator before and want to start a new calculation but the data is still there from my previous project, how do I clear the data?
If you have registered with the Calculator you can start a new calculation by logging in and clicking the 'Start a new project' button. If you are not registered you will have to clear the cookies out of your browser to reset the system.