Rheem Stellar 50L Owner's Manual And Installation Instructions page 15

SATURATION INDEX
The saturation index is used as a measure of the water's corrosive or scaling
properties. The saturation index figures stated are calculated using a water
temperature of 80°C.
In a corrosive water supply, the water can attack copper parts and cause them
to fail. Where the saturation index is less than –1.0, the water is very corrosive
and the Rheem warranty does not apply to a copper sheathed heating unit. A
corrosion resistant heating unit must be used for the Rheem warranty to apply to
the heating unit. This water heater is supplied fitted with a corrosion resistant
heating unit.
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.
Where the saturation index exceeds +0.80, the Rheem warranty does not apply
to a stainless steel cylinder or a standard watts density heating unit. A low watts
density heating unit must be used for the Rheem warranty to apply to the heating
unit.
Water which is scaling may be treated with a water softening device to reduce
the saturation index of the water. Contact Rheem Service or their nearest
Accredited Service Agent if a replacement heating unit is required.
Refer to the Saturation Index chart
connection detail on page
-1.0
very corrosive
29 for the position of the expansion control valve.
SATURATION INDEX (SI)
ELECTRIC WATER HEATERS - STAINLESS STEEL
WITHIN WARRANTY
SPECIFICATION
SATURATION INDEX
(calculated @ 80°C water temperature)
corrosive
15
on page 15. Refer to the
0 +0.4
very scaling
scaling
WATER SUPPLIES
cold water
+0.8