I have an instant tankless water heater, stibel-eltron dhc12, and want to protect the heating element from the high mineral content in my water.

A simple strainer may be good enough or a filter. What can I simply install on the supply side, which is 1/2" braided line?

  • When in doubt, filter it out. Really the bigger issue is the resulting pH
    – Tyson
    Mar 24, 2017 at 0:35
  • Re comment above: you've told us you have high mineral content, but without a water analysis it's impossible to tell you what to do
    – Tyson
    Mar 24, 2017 at 0:36
  • Oh gosh, I don't know my water analysis results. I just want to filter the water from going in. Live in Joshua Tree which get water from the ground. I think even a strainer would help, no?
    – user22980
    Mar 24, 2017 at 0:59
  • Although my pH was around 7.5 I believe
    – user22980
    Mar 24, 2017 at 0:59
  • 1
    The minerals in the water are in solution; no filter is going to remove them. The only way to reduce them is by a "water softener" which is expensive and troublesome. Personally I wouldn't bother with an additional filter, the unit already has one. stiebel-eltron-usa.com/sites/default/files/pdf/… If the manufacturer of your tankless heater has a descaling procedure, then you could do that every 3 years to 5 years depending on how much scale builds up. Mar 24, 2017 at 1:48

1 Answer 1


Your heater doesn't have a recommended limit on hard water, but I've seen others ranging from saying 7 to 12 gpg (grains per gallon) max. You need to find the hardness of your water before doing anything.

You can purchase hardness test strips, which are the easiest way to figure this out.

enter image description here

Water Hardness Scale

Grains Per Gallon   Milligrams Per Liter (mg/L)    Classification
                    or Parts Per Million (ppm)   
-----------------   ----------------------------   -------------------
less than 1.0       less than 17.1                 Soft
1.0 - 3.5           17.1 - 60                      Slightly Hard
3.5 - 7.0           60 - 120                       Moderately Hard
7.0 - 10.5          120 - 180                      Hard
over 10.5           over 180                       Very Hard


Hard water is mainly caused by calcium and magnesium carbonates.

The most common way to treat it is with a softener, where "hardness ions" are exchanged for sodium ions in an ion-exchange resin. Essentially, the hardness is swapped with salt.

Typical water softener


Your manufacturer should also have some cleaning instructions, where you periodically clean the heater elements. This is probably every 1-5 years depending on water quality.

  • Yes! Awesome. My gpg's were 20-40% over limits. If more exact details are needed I'll have to dig results or new test. Thank u
    – user22980
    Mar 24, 2017 at 3:25

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