How to complete the Water Efficiency Calculator for Building Regulations Part G Compliance
This article explains the following with respect to the water efficiency calculator;
- What the water efficiency calculator is
- The purpose of the calculator
- Where the requirements are specified
- What projects the calculation method applies to
- How to use the calculator
What is the water efficiency calculator?
The water efficiency calculator is a standard calculation method set out in the Building Regulations Part G. The calculator uses properties and quantities of sanitaryware and appliances to estimate water consumption per occupant in new build dwellings. The purpose of this being to limit water consumption within new dwellings to below 125 litres per person per day, as calculated using the this standard method. The water efficiency calculator method is set out in Appendix A of approved document Part G which you can download from the Government Planning Portal website, www.planningportal.co.uk.
Does the water efficiency calculator apply to your project?
To comply with the Building Regulations Part G, new build dwellings must have an estimated daily water consumption of 125 litres per person, or less. However, this consumption requirement can be further tightened to 110 litres per person, depending on the decision of the local planning authority.
There are two ways to demonstrate compliance with the water consumption requirements, the first is to only select fittings and appliances that conform the the requirements in Table 2.1 or Table 2.2. Which table depends on whether the dwelling is required to meet the 125 or 110 litres per person per day estimated water consumption.
The second method to demonstrate compliance, is to use the water efficiency calculator method. This calculator method must be used if any of the following apply;
- Any 1 or more fittings/ appliances do not meet the requirements set out in table 2.1 or table 2.2 (depending on which one applies)
- If a shower is not being provided
- When a water softener is being installed
- When a waste disposal system is being installed
- When a water re-use system is being installed
Table 2.1 contains the maximum consumption figures required to comply with 125 litres a day per person estimated consumption- on page 16 of approved document G.
Table 2.2 contains the maximum consumption figures required to comply with 110 litres a day per person estimated consumption- on page 17 of approved document G.
How to use the calculator
The Part G water efficiency calculation method uses a simple spreadsheet. The spreadsheet is shown in PDF format within Appendix A of Approved Document G. You could use excel to create your own, or save yourself hours (if not days) by downloading the Building Service Portal free version available here. For simple systems, only table A1 is required, shown below. To complete table A1, simple enter the capacity or flow rate for each fitting in the table that apply to your project. These figures then need to be times by the relevant use factors set out in the table, and fixed use factors added. This gives you the figures needed to populate column 4. From here, the answers to column 4 are to be summed to give line 5. Then there are simple equations given to calculate lines 9 & 11, 11 being the final estimated water consumption per person, per day.
If you are using the Building Services Portal spreadsheet template, the figures you are required to input are clearly shown in yellow and all the calculations are performed automatically. So all you need to do is input the various capacities and flow rate figures. Just click to download the free version now. The spreadsheet also includes the Building Services Portal guidance notes to help you through every step.
More complex systems
Multiple fittings or appliances of the same type
The calculations do get slightly more complicated for systems that have multiple fittings or appliances of the same type. For each fitting/ appliance type with multiples being installed, a second table must be filled in. For example, for multiple tap types, Table A2.1 is to be completed which calculates both the ‘average flow rate’ and ‘proportionate flow rate’, the greater of which is to be entered into the main table, table A1.
Water softeners and rainwater/ grey water recovery systems
There are also separate tables to be completed for dwellings with water softeners and rainwater/ grey water recovery systems. Rainwater and grey water recovery systems can be used to lower the water consumption estimates for properties with high water usage fittings and appliances, in order to comply with the regulations.
The additional tables required to be completed for the more complex systems, all result in figures required to be entered into the main table, table A1. Once table A1 is complete, the calculation for the estimated water consumption per person, per day can be calculated from the simple formulars. All the tables are included within the Building Services Portal spreadsheets, and all calculations are automatically calculated according to the regulation guidlines.
If the calculated, estimated water consumption per person per day is not compliant to the requirements, then improvements need to be made by either changing fitting/ appliance types or by increasing rainwater/ grey water recovery capacity.
Your water efficiency calculations can be professionally presented with the Building Services Portal Premium Water Efficiency Calculator, which has watermarks removed and your company logo included. Ideal for submissions to Building Control to demonstrate Building Regulation Compliance for your projects.
