Where can I find information on water hardness?

Hardness

Hardness is commonly referred to as the ability of your water to neutralize soap, or the inability of the water to form soap lather.
Hard water can cause scale to form on hot water pipes, boilers, and household appliances; cause a scum to form on your tea or coffee; and sometimes give a dingy appearance to your laundry.
Hard water is not known to be a health hazard, even in high concentrations. In fact, it is better for drinking as the calcium and magnesium in hard water are good for bones and teeth.

Water Softeners

Water treatment units designed to remove hardness are called water softeners. These units remove calcium and magnesium ions from the water by exchanging them for sodium ions.
Water flows through an ion exchange resin which is composed of synthetically-produced solids in bead form, generally about 1/64 to 1/32 diameter. These beads have extremely fine pores that are charged with sodium ions and it is at these sites where the ionic exchange takes place. The calcium and magnesium are traded for sodium. Once all the exchange sites in the resin have been used, the capacity of the resin is exhausted.
The ion exchange process is reversible and the resin can be regenerated to its original capacity and will be ready for another cycle. The resin is charged with sodium by adding common salt (sodium chloride) to the water softener.
Only water to be heated and cold water used for laundry and washing need to be softened. Flush toilets use a large amount of water and from an economic stand point it would be wasteful to treat this water.
A tap with cold, unsoftened water should be maintained for drinking purposes. Softened water may also be harmful to animal and plant life so it should not be used for aquariums or for watering lawns, plants or gardens.
Water softeners increase the sodium level in the water. Therefore, people with heart conditions or high blood pressure (people on a low-sodium diet) should consult their doctor before drinking softened water.