Rheem Gas Domestic Indoor Water Heater Installation And Owner's Manual page 15

WATER SUPPLIES
SATURATION INDEX
The saturation index (SI) is used as a measure of the water‟s corrosive or
scaling properties.
In a corrosive water supply, the water can attack copper parts and cause them
to fail.
In a scaling water supply calcium carbonate is deposited out of the water onto
any hot metallic surface.
Where the saturation index exceeds +0.40, the water is very scaling. An
expansion control valve must be fitted on the cold water line after the non-
return valve to protect and for the Rheem warranty to apply to the temperature
pressure relief valve and water heater cylinder.
Water which is scaling may be treated with a water softening device to reduce
the saturation index of the water.
Refer to the Saturation Index chart on page 15. Refer to the cold water
connection detail on page 29 for the position of the expansion control valve.
SATURATION INDEX (SI)
GAS STORAGE WATER HEATERS
WITHIN WARRANTY
SPECIFICATION
-1.0 0 +0.4 +0.8
SATURATION INDEX
(calculated @ 80°C water temperature)
scaling
very corrosive corrosive very scaling
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