Water Hardenss.

Frank in FL

Well-known member
Jul 3, 2019
I just had my water tested.
The water coming directly out of my spigot is reading 271 for hardness.
The water in my pool is reading 539.

What would cause the water in the pool would be significantly higher than what comes out of my spigot ?


LifeTime Supporter
TFP Guide
Feb 6, 2015
Chandler AZ
Evaporation - as your pool water evaporates, it leaves the calcium behind. Adding new water to replace that which evaporated adds more calcium to the water.


Well-known member
May 27, 2017
Coventry, CT
On a first fill your pool water has the same hardness as your fill water.

Then pool water evaporates and the calcium stays leaving you with a lower volume of water with a higher concentration of calcium hardness. The only water to get back to the original volume and concentration of calcium hardness is to add water with no calcium in it at all, like distilled or RO water.

More practically, you'll be using more spigot water to refill the pool, this adds more calcium. Thus it's expected that calcium hardness generally increases.