Rheem 491 Owner's Manual And Installation Instructions page 20

WATER SUPPLIES
CHANGE OF WATER SUPPLY
The changing or alternating from one water supply to another can have a
detrimental effect on the operation and / or life expectation of a water heater
cylinder, a temperature pressure relief valve and a heating unit.
Where there is a changeover from one water supply to another, e.g. a rainwater
tank supply, bore water supply, desalinated water supply, public reticulated water
supply or water brought in from another supply, then water chemistry information
should be sought from the supplier or it should be tested to ensure the water
supply meets the requirements given in these guidelines for the Rheem warranty
to apply.
SUMMARY OF WATER CHEMISTRY ADVICE AFFECTING WARRANTY
The water heater and its components are not suitable for certain water
chemistries. Those chemistries are listed below. If the water heater is connected
at any time to a water supply with the following water chemistry, the Rheem
warranty will not cover any resultant faults on the components listed below:
Water Chemistry
Total Dissolved Solids (TDS) > 2500 mg/L
Total Dissolved Solids (TDS)
not suitable for anode type
Saturation Index (SI) < -1.0
Saturation Index (SI) > +0.4
(if expansion control valve is not fitted)
Saturation Index (SI) > +0.8
Component
water heater cylinder
water heater cylinder
copper sheathed heating unit
water heater cylinder
temperature pressure relief valve
standard watts density heating unit
20