75Water Softening
Water softening is a method of removing from water the minerals that make it hard. Hard water
does not dissolve soap readily. It forms scale in pipes, boilers, and other equipment in which it is
used. The principal methods of softening water are the lime soda process and the ion exchange
process.
In the lime soda process, soda ash and lime are added to the water in amounts determined by
chemical tests. These chemicals combine with the calcium and magnesium in the water to make
insoluble compounds that settle to the bottom of the water tank.
In the ion exchange process, the water filters through minerals called zeolites. As the water
passes through the filter, the sodium ions in
the zeolite are exchanged for the calcium and
magnesium ions in the water, and the water is
softened. After household softeners become
exhausted, a strong solution of sodium
chloride (salt) is passed through the filter to
replace the sodium that has been lost. The
use of two exchange materials makes it
possible to remove both metal and acid ions
from water.
Some cities and towns, however, prohibit or restrict the use of ion exchange equipment on drinking
water, pending the results of studies on how people are affected by the consumption of the added
sodium in softened water. The containers hold the resin for the deionization. Calcium and
magnesium in water create hard water, and high levels can clog pipes. The best way to soften
water is to use a water softener unit connected into the water supply line. You may want to consider
installing a separate faucet for unsoften water for drinking and cooking. Water softening units also
remove iron.
The most common way to soften household water is to use a water softener. Softeners may also
be safely used to remove up to about 5 milligrams per liter of dissolved iron if the water softener is
rated for that amount of iron removal. Softeners are automatic, semi-automatic, or manual. Each
type is available in several sizes and is rated on the amount of hardness it can remove before
regeneration is necessary. Using a softener to remove iron in naturally soft water is not advised; a
green-sand filter is a better method. When the resin is filled to capacity, it must be recharged. Fully
automatic softeners regenerate on a preset schedule and return to service automatically.
Regeneration is usually started by a preset time clock; some units are started by water use meters
or hardness detectors.
Semi-automatic softeners have automatic controls for everything except for the start of
regeneration. Manual units require manual operation of one or more valves to control back washing,
brining and rinsing. In many areas, there are companies that provide a water softening service. For
a monthly fee the company installs a softener unit and replaces it periodically with a freshly charged
unit.
The principle behind water softening is really just simple chemistry. A water softener contains resin
beads which hold electrically charged ions. When hard water passes through the softener, calcium
and magnesium ions are attracted to the charged resin beads. It's the resulting removal of calcium
and magnesium ions that produces "soft water."