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Water Quality Standards
and Recommendations
Permissible (PPM) Desirable (PPM)
Microbiologicals
(algae, bacteria, fungi) 0 0
Inorganic Chemicals
Calcium <40 <0.6
Chloride <250 <25
Copper <1.3 <1.0
Iron <0.3 <0.1
Lead <0.015 0
Magnesium <12 <0.1
Manganese < 0.05 <0.03
Nitrates\Nitrites <10 as N 0
Potassium <20 <0.3
Silicate <25 <1.0
Sodium <20 < 0.3
Sulfate <250 <50
Hardness <17 <0.05
Total Dissolved Solids <50 <10
Other Parameters
pH 6.5-8.5 7-8
Resistivity 0.01* 0.05-0.1*
* Megohm-Cm (Compensated to 25°C)
Unfavorably high total ionized solids (TIS) can
accelerate the rate of galvanic corrosion. These
contaminants can function as electrolytes which
increase the potential for galvanic cell corrosion and
lead to localized corrosion such as pitting which can
be observed at the studs and on the outside surface
of cooling coils. Eventually, the pitting will become
so extensive that the coil will leak refrigerant into the
water reservoir.
As an example, raw water in the United States
averages 171 ppm (of NaCl). The recommended
level for use in a water system is between 0.5 to 5.0
ppm (of NaCl).
Recommendation: Initially fill the tank with distilled/
deionized water. Do not use untreated tap water as
the total ionized solids level may be too high.
Maintain this water quality at a resistivity of between
1 to 10 megohm-cm (compensated to 25°C) by
using a purification system. Although the initial fill
may be as high as 10 megohm-cm (compensated to
25°C), the desired level for long time usage is 1 to 3
megohm-cm (compensated to 25°C).
The above two recommendations will reduce the
electrolytic potential of the water and prevent or
reduce the galvanic corrosion observed.
15.00
10.00
3.00
1.00
0.10
0.05
Resistivity (megohm-cm @ 25°C)
Not Recommended, Increasingly Corrosive
Operations with Stainless Steel Systems
Operations with
Mixed Metals
Copper/Brass/
Stainless Steel
CONSULT MATERIALS ENGINEER
10 20 30 40 50 60 70 80
Water Quality Considerations
°C
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