EcoWater CHC Series, Service And Troubleshooting Manual

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97
Waters are commonly classified in terms of the degree of hardness. There are different standards, as
listed in the following Table:
Table: Water hardness Classification
Developed by Water Quality Association
Term ppm as CaCO
3
Soft < 17.1
Slightly hard 17.1 – 60
Moderately hard 60 – 120
Hard 120 –180
Very hard > 180
The hardness of water is derived largely from contact with the soil and rock formations. Rain water as
it falls upon the earth is incapable of dissolving the tremendous amounts of solids found in many
natural waters. The ability to dissolve is gained in the soil where carbon dioxide is released by bacterial
action. The soil water becomes highly charged with CO
2
, which, of course, exists in equilibrium with
carbonic acid. Under the low pH conditions that develop, basic materials, particularly limestone
formations, are dissolved. The Figure below shows where this originates and how it attacks carbonate
minerals. Since limestone is not pure carbonate but includes impurities such as sulfates, chlorides, and
silicates, these materials become exposed to the solvent action of water as the carbonates are dissolved,
and they pass into solution too.
In general, hard waters originate in areas where the topsoil is thick and limestone formations are
present. Soft waters originate in areas where the topsoil is thin and limestone formation is sparse or
absent.
LIMESTONE
Zone of intense chemical reaction
CaCO
3
+ H
2
CO
3

Ca(HCO
3
)
2
,
MgCO
3
+ H
2
CO
3

Mg(HCO
3
)
2
SUBSOIL
Zone of less bacterial action

CO
2
in small amounts
Continued action on basic compounds – CaCO
3
+ H
2
CO
3

Ca(HCO
3
)
2
,
etc.
TOPSOIL
Zone of intense bacterial action

CO
2
in large amounts
Some action on basic compounds – CaCO
3
+ H
2
CO
3

Ca(HCO
3
)
2
, etc.
Rain