Can you adjust the residual hardness of a water softener?

There are two persistent assumptions circulating regarding residual hardness: that you should always maintain a minimum residual hardness, and that this is even a legal requirement. In this blog, you can find out whether you can set a residual hardness for a water softener, and what the regulations actually say on the matter.

Can you set a residual hardness level on a water softener?

Yes. All Mooiwater water softeners come fitted with a mixing valve as standard. This allows us to precisely set any desired residual hardness level, for example 2dH instead of 0dH.

Is a minimum residual hardness required by law?

No, that is a misunderstanding. It is sometimes claimed that the Drinking Water Decree stipulates a minimum residual hardness, but no such requirement exists. Older regulations contained, at most, a recommendation, but never a requirement.

What do the Waterwerkbladen say about residual hardness?

The old Water Worksheet published by the Association of Drinking Water Companies (Worksheet 4.6.3, June 2004) recommended ensuring a residual hardness of 5.6dH. There is no longer any mention of this in the current Water Worksheet (Worksheet 4.6.4, January 2017): no monitoring programme is required for domestic water systems, and no specific requirements are now imposed on drinking water quality. The water companies have therefore themselves retracted their own recommendation.

Why on earth would you set a residual hardness?

The question isn’t whether it’s possible, but why you’d want to. With lower residual hardness, you’ll experience less limescale build-up and it will take longer for appliances to become encrusted and your bathroom to look dull, but it will still happen eventually. If you nevertheless wish to maintain a certain level of residual hardness, for example 2dH, we can arrange that without any problems. You can read more about what limescale-free water means for your pipework on our page about or Soft water corrodes copper pipes.