It seems that the terms TDS and Hardness are often confused.
We measure the water coming from the RO system for TDS and compare it to the TDS reading coming from the water source. The formula is:
Incoming - Outgoing / Incoming
A 90% rejection rate or better means that the membrane on the RO system is working.
Hardness is used to measure if the water softener is working. Knowing how hard the water is before running through the softener is the key to knowing if the water softener is working. A reading of one grain of hardness is considered soft, but if the reading is lower grains than the incoming water, the softener is doing its job. It is important to find out the average readings in your area.
Here is a handy chart to help compare the two readings.
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