Water Treatment Devices
Hard water:
While water is in the ground, it picks up soluble bits of whatever it passes through. While this can mean contamination that makes the water unfit to drink, in many cases it simply means that the water contains minerals found in the earth, making the water "hard". Hard water poses no health hazard. Hard water usually has a lot of calcium or magnesium dissolved in it, and can cause two problems:
- Scale: It can cause "scale" to form on the inside of pipes, water heaters, tea kettles and so on. The calcium and magnesium precipitate out of the water and stick to
things. The scale doesn't conduct heat well and it also reduces the flow through pipes. Eventually, pipes can become completely clogged, and the efficiency and life of a water heaters can be reduced.
- Soap scum: It reacts with soap to form a sticky scum, and also reduces the soap's ability to lather. Since most of us like to wash with soap, hard water makes a bath or shower less productive.
The most common solution to hard water is to use a water softener.
How it works: The most common type of water softener is an ionic exchange water softener. This type uses salt (sodium chloride) to remove the hardness from water. The calcium and 
magnesium ions in the water are replaced with sodium ions. Since sodium does not precipitate out in pipes or react badly with soap, both of the problems of hard water are eliminated. To do the ion replacement, the water in the house runs through a bed of small plastic beads. The beads are covered with sodium ions. As the water flows past the sodium ions, they swap places with the calcium and magnesium ions. The water with the sodium ions then travels on to the house.
Eventually, the beads contain nothing but calcium and magnesium and no sodium, and at this point they stop softening the water. It is then time to regenerate the beads. Regeneration involves soaking the beads in a salty "brine" solution. You add salt to a water softener, and salt is sodium chloride. The water softener mixes up a very strong brine solution and flushes it through the beads. The strong brine displaces all of the calcium and magnesium that has built up in the beads and replaces it again with sodium. The remaining brine plus all of the calcium and magnesium is flushed out through a drain pipe.
Health Concerns:
Hard water poses no health hazard. On the other hand, the sodium that remains in softened water may be a problem for those on sodium-restricted diets. Other people simply may wish to avoid the slightly salty taste of treated water. In either case you can install a separate water dispenser that bypasses the softener. You also can use potassium chloride instead of salt, although this costs about three to four times more.
Additional Information:
Certification of Residential Water Treatment Devices
When a manufacturer claims that a drinking water treatment device will reduce contaminants; such as lead, Cryptosporidium (protozoan cysts), pesticides, herbicides, solvents, heavy metals, bacteria and viruses, or makes other health related performance claims, the device must be certified by the DHS, pursuant to Health & Safety Code Section 116830. DHS does not regulate devices that make aesthetic claims. Aesthetic claims include improvement in taste, odor and appearance. Also, DHS does not regulate backpacking or camping filters, sports bottles, shower filters or water softeners.