Hard Water and Soft
Soft Water

Some areas have what is commonly referred to as "hard water" which is a a home
water softener.

Water softening is essentially the exchange of sodium for the calcium and
magnesium minerals present in the water (which cause the hardness).  As the
water softener processes the hard water on a daily basis, the treatment capability
of the softener becomes depleted and must be recharged or regenerated.

Regenerating the unit uses a large quantity of sodium-rich water, called "brine",
that must be disposed of. In homes with onsite septic systems, this brine flows
into the septic tank and eventually makes its way to the system's drainfield.