Water filters that tie-in directly to a home's water line or sit at the end of the pipe network are known as point-of-use water filters, a group that also includes pitcher water filters. For people who don't want the hassle of carting jugs or dispensers to and from the refrigerator, under-sink and faucet-mount point-of-use systems are a good alternative.
One minor downfall is that water coming from these filters won't be as chilled as if it had been stored in the fridge, so people who prefer their water to be ice cold might not find them a good fit.
Faucet-mount water filters
A number of companies, such as PuR and Culligan, make filtering units that screw onto existing faucets in the kitchen or bathroom. Faucet-mounted filters are an oblong shape that is either horizontally or vertically placed. When purified drinking water is required, a switch allows water to flow through the filter. When water is for cooking or other non-drinking needs like washing dishes, the filter is bypassed, providing regular tap water and saving you from filtering water unnecessarily. Faucet-mount units generally cost between $20 and $40 and filters can last between three months and a year. Many can treat 100 gallons of water before needing to be replaced. The more a faucet-mount filter fills with contaminants, the slower water will come out.
Under-sink water filters
These water filters should be installed by a professional, or at least by someone with sufficient know-how. They attach to the cold water line and purify all water traveling through. Some, known as in-line filters, filter all water that comes through the regular tap. Others, known as line-bypass filters, divert water to a second tap that is just for drinking water. These systems may or may not come with a separate faucet. They usually deliver water more quickly than faucet-mount systems and aren't as likely to clog, but the cost for an under-sink model will be much higher. The better (and more expensive) systems utilize reverse osmosis for filtration. They do, however, deliver water very slowly and create a lot of waste. Most under-sink water filters cost between $80 and $100, with yearly expenses for filters similar to those for pitcher filters.