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Sizing Your Water Softener

What size water softener do you need?

To find out what size water softener meets your requirements, you need to work out the following:

  1. The hardness of your water supply (in parts per million of hardness (ppm))
  2. The regeneration volume of the softeners
  3. The volume of softened water you require per day

Once you know this, you’ll be able to work out whether an 8L10L or 20L softener is best for the size of your home or office Water hardness

Water hardness

To find out what your water hardness is, have a look on your water supplier’s website and look up water quality. The website will request your post code and a report will open listing your water quality including your water hardness.

You should be given a figure either in ppm or Clark degrees. In the case of the water that is supplied to The Healthy House™, the hardness level is listed as 15.05 Clark degrees. Severn Trent does not list the ppm so using the conversion figure of 14.3 our ppm figure is calculated 15.02 x 14.3 = 215ppm.

Volume of water between softener regenerations

Now that you know your water hardness in ppm, you can work out how many litres of hard water our softeners can process before needing to go through a ‘regeneration’.

A regeneration is the self-cleaning process a water softener carries out. If you have a water softener installed, when you turn on your tap, hard water runs through a tank of ion exchange resin. This process removes the calcium and magnesium (limescale) that makes your water hard, as it bonds loosely to the resin. When the resin becomes ‘full’ of the hard water deposits, a mixture of salt and water flows through it to flush them away, completing the regeneration process.

Each regeneration process uses a certain amount of water and salt. The smaller the softener, the fewer litres of hard water it can soften before needing to go through the regeneration process (this is the regeneration volume). Therefore, to avoid wasting excess water and salt, it is important that you choose an appropriately sized softener for the volume of water you use each day.

For the softeners that we offer, the regeneration volumes are as follows:

8L Softener =           1330L of hard water*
10L Softener=         1660L of hard water
20L Softener=         3300L of hard water

*Based on 300ppm (also written as 300CaCO3mg/l)

The volume of softened water required per day

The regeneration volumes for our softeners are based on 300ppm, which indicates very hard water. Therefore, unless your water hardness is 300ppm, you need to use a conversion factor to size the softener for your water hardness.

To find the conversion factor, divide 300 by your ppm figure from step 1 (for example, ours is 215ppm). The conversion factor (or multiplier) for our water is 300 ÷ 215 = 1.4.

Multiply the conversion factor by the regeneration volume of the softener at 300ppm (see step 2) to give the regeneration volume for your specific water hardness.

For example:

8L       1330 x 1.4 = 1862L between regenerations
10L     1660 x 1.4 = 2324L between regenerations
20L     3300 x 1.4 = 4628L between regenerations

Size of household

The average volume of water that a person will use in a day is 160 litres, so a 3 person household will use around 480L per day. Therefore, the individual softeners will be regenerated in the following number of days given the hardness level of 215ppm at The Healthy House:

8L       1862/480 = 4 days approx
10L     2324/480 = 5 days approx
20L     4628/480 = 10 days approx

To size the best softener for your usage it is important to consider the physical size of the unit in relation to the size of the space that you have, the number of people in your household and the frequency of the regeneration. It is important to remember that each time the softener regenerates it uses a certain amount of water and a certain amount of salt. The amount of salt that is used per regeneration is as follows:

8L       1.2kg
10L     1.5kg
20L     3.0kg

Sizing your softener

Based on the fact that each regeneration costs money in salt and water, we normally recommend that you look for a softener with a minimum of a 3 day regeneration process. Ideally, we recommend you opt for the largest softener that your available space and budget allows. 

If you have any questions about sizing a softener for your needs, don’t hesitate to give us a call on 0845 450 5950 and we can go through the calculations with you.