“Water treatment” refers to any modification made to raw water (water from an original source, such as a lake or river). Although they both fall under the term “water treatment, water filters are mainly used to provide clean, contaminant-free water for drinking and other purposes, while water softeners are mainly used to remove “hardening” minerals like calcium and magnesium from the water; water softeners do not remove dangerous chemicals or bacteria.
Water is termed “hard” if it contains large amounts of dissolved calcium and magnesium. Hard water causes two major problems. First, it can initiate scaling on the inner surface of pipes, water heaters, and tea kettles. When scaling occurs, the calcium and magnesium separate from the water and form a hard, thin layer on the inside of such appliances, causing the appliances to clog and reducing their ability to conduct heat. Second, hard water causes soap scum to build up on dishes and tile. Hard water also reduces the soap’s ability to lather.
In order to remove calcium and magnesium from water, water softeners replace the calcium and magnesium ions with sodium ions. Because sodium does not separate and scale on appliances or react badly with soap, both problems stemming from hard water are solved. However, calcium and magnesium are better for our health than sodium. Water filters will generally solve the same problems as water softeners, without adding sodium to the water.