What is the difference between water softening, filtering and purifying? Some people use those terms almost interchangeably, but they attack different problems with different technologies.
Water softeners: These products deal with “hard water,” which basically means your water supply has an excess of minerals like magnesium and calcium. If you notice white chalky deposits inside your dishwasher and other water-using appliances or the inside of your pots and pans you may have hard water. You’ll also notice spots on your glassware and a “slimy” feel to your shower water. Hard water is not necessarily unhealthy though. In fact, our bodies require minerals like magnesium and calcium in small doses. However, besides tasting bad and corroding household appliances, over time hard water will build up deposits on the inside of your plumbing pipes, creating what we refer to as “lime scale.” This will lead to corrosion and blockages.
Two basic types of water softeners are available: salt-based and salt-free. Salt-based systems are more effective in removing minerals like calcium and magnesium, but are more expensive and require regular maintenance. Salt-free systems don’t really remove minerals but use electricity or magnetism to neutralize them so they don’t stick to surfaces. Also referred to as “water conditioners,” salt-free systems are less expensive to install and maintain, although they may not do much to prevent lime buildup. Salt-free systems also appeal to people who don’t like adding chemicals to their water.
Water filters: Filtration comes in a variety of technologies to remove contaminants besides hard minerals that find their way into even the best water systems. The EPA has established Maximum Contaminant Levels (MCLs) for various chemicals and compounds, which for the most part makes tap water safe to drink almost everywhere. Your local water utility is required by law to give you the MCL levels. Nonetheless, some water systems skirt the danger zone of substances such as arsenic, lead, mercury, phosphates, carbonates, nitrates, sulfates and even potentially poisonous gases like cyanide and radon, or proven cancer-causing chemicals like benzene, vinyl chloride and trihalomethanes.
Filtration systems are available in a variety of technologies to remove these potentially harmful contaminants from your water. At the high end are whole-house filtration systems that connect to your main water line and solve a wide range of issues affecting your water quality, taste and appearance. Less expensive systems can be installed that intercept incoming water under the sink or at faucets.
Water purifiers: Filtration vs. purification is to some extent a matter of semantics. The best water purification systems take filtration a step farther by also filtering out microscopic disease-causing pathogens like cryptosporidium, giardia, legionella and a host of viruses. It is rare, though not unheard of, for any of these to make it into tap water. Occasional conditions arise that lead to outbreaks that cause sickness and even death to small parts of our population. The smaller the contaminant the harder they are to remove, which is why the most sophisticated purification systems tend to be the most expensive.