How do I fill in the ‘water softeners’ section of the Water Efficiency Calculator in the government’s Code for Sustainable Homes?

Below is a guide to calculating your household figures to comply with the Code for Sustainable Development:


The section on ion exchange water softeners (h.) asks for four figures:

1) Total capacity used per regeneration (%)

2) Water consumed per regeneration (litres)

3) Average number of regeneration cycles per day (No.)

4) Number of occupants served by the system (No.)

We’ve put together figures which represent an abnormally high usage of water in a very hard water area.

1) 3.27%

2) 17 litres

3) 1.15 regenerations per day

4) 5 people

Here’s how we worked out the above answers.

A Harvey Water Softener™ uses 17 litres of water to regenerate. The water softener will regenerate itself when a certain amount of water has passed through it. The amount of water is determined by a gear setting that will be set on installation, based on the local water hardness.

Using a higher level of hardness than in most English homes, 315 ppm, the gear setting would allow 520 litres of water to pass through the water softener between regenerations.

This gives us our answers for questions one and two:

1) 3.27%

2) 17 litres

The number of occupants served by the system will vary from house to house but we’ve used a higher figure of five occupants using the water system.

3) 5 people

A Harvey Water Softener™ only regenerates when a household has used a certain amount of water. We cannot give an average number of regenerations per day without first estimating how quickly the occupants of the house will use water.

This will depend on some of the other water efficiency figures that you’ll be working out – how many baths and showers, what kind of washing machine, etc.

We have used another high estimate of 120 litres per person per day. Multiplying this by our example of five people in the household and dividing it by the 520 litres of water the softener softens before regenerating, it allows us to calculate the answer to question three:

4) 1.15 regenerations per day

The Water Efficiency Calculator puts all these numbers into a formula and works out how much water is being used beyond the 4% good practice level.