And there are several main technologies, including GAC , reverse osmosis and distillation . Finally, beware of the goldfish trick, as not all plumbing contractors are scrupulously honest. It is almost impossible to say before installing the system and sending the filtered water to a testing company for verification. Because of the nature of the technology, and because of variability in plumbing systems, it is difficult for manufacturers to design one type of water system for the entire country. What's more, because filters work at high pressure, with a variety of tiny openings, they can be sensitive to hard water, hot water, cloudy water, and various other ways in which water in one city may vary widely from water in another.
Filters are also prone to clog and malfunction, as consumer magazines have detailed.
The best advice is to contact a plumbing contractor experienced in the installation of such systems. At least 25 percent of bottled waters come from municipal sources. In some regions of the country, where city tap water is of excellent quality and bottled water is only marginal, you might actually do worse with stuff from the supermarket. But by reading labels carefully, you might be able to determine how the water was bottled, and whether it is superior to what is coming out of your tap. For definitions of which terms are significant and which are not, check our glossary .