Water purifier/deionizer?

from marine depot: http://www.marinedepot.com/Aquarium_Pharmaceutical...

How many gallons of water will the Tap Water Filter make?

The amount of deionized (DI) water produced by the Tap Water Filter depends entirely on the level of minerals, heavy metals, phosphate, nitrate, etc. that is in your tap water. Each cartridge has a fixed ion exchange capacity. In New York City, for example, aquarists can produce up to 300 gallons of DI water with a single cartridge. An aquarist in northern New Jersey, however, made 15 gallons of water. An analysis of the NJ water showed very high levels of copper, zinc, phosphate, nitrite, and nitrate in addition to the normal hardness minerals. A heavily polluted water source will use up a cartridge much sooner than a water supply low in minerals and pollutants. Most aquarists produce somewhere between 50 and 150 gallons per cartridge.

The deionized water is the form of distilled water that is free from all types of mineral salts from water. These mineral ions include sodium, calcium, iron, copper, chloride, and bromide

A water purifier on the other hand has a membrane that removes the excess of the minerals added in the water.

The best option to remove TDS from water is to use hard water softener. A hard water filter, also called a water softener, is designed to filter water to remove excess minerals such as magnesium and calcium that are present in the hard water.

The activated carbon hard water filter creates generally odor-free, pleasant drinking water.