You insure your home, your car, and your jewelry. Why not the safety of your family's water supply? Sure, public water systems filter out contaminants to meet standards set by the Environmental Protection Agency, and private wells may be screened by local health departments for bacteria and nitrates. (If you're among the 10 to 20 percent of Americans who draw their water from a private well, the only way to know everything that's in it is to have it tested by a certified lab.) But even though town and city water-quality reports are available to the public, they can't tell you everything about the water coming out of your faucets. If your pipes are releasing lead, for instance, a municipal report won't show that.

No matter what the source, a home filtration system can purify your water further. Whether you need to eliminate contaminants or just correct a funny smell, there's a filter that can do the job.

Problem: I want ice-cold drinking water on hand all the time.

Filtration System: Pitcher
How It Works: You fill the pitcher, then store it in the refrigerator. Activated carbon, metal-scavenging agents, and size-exclusion filters remove contaminants.
Facts:
Pros: Easy to use; nothing to install.
Cons: Fewer gallons per filter cartridge than other types; inconvenient to keep full; filters require frequent changing (about every two months).
Where to Buy: Pur Ultimate large-capacity pitcher, $30, at most major retail stores. See www.purwater.com for on-line retailers. Replacement filter: $20.

Problem: My family likes to drink water all day, but the pitcher-style filters are too heavy for my kids.

Filtration System: Faucet mount
How It Works: Faucet-mounted filters either replace the faucet aerator or screw on over it. They duplicate some or all of the filtration technologies used in pitchers.
Facts:
Pros: Easy to install.
Cons: May work slowly; cartridges require frequent changing (at least every two to three months), and filtration can slow further with extended use.
Where to Buy: Chrome Brita On Tap filter, $30, at most major retail stores. See www.brita.com for on-line retailers. Two-pack of replacement filters: $30.

Problem: My family drinks lots of water, but a faucet-mounted filter is too slow.

Filtration System: Under sink
How It Works: These filters hook into the cold-water line under the sink and need to be attached to a wall or cabinet back. Filtered cold water is drawn through a separate faucet.
Facts
Pros: Filters quickly; cartridges can be long-lasting (change every three to six months).
Cons: Usually requires professional installation; filter cartridges can be hard to change.
Where to Buy: Culligan Plumbed-in Under-sink Filter (includes faucet), $30, plus about $119 for installation; www.sears.com. Replacement filter: $11.

Problem: Our water comes from a private well, and I want the water we use for cooking and drinking to be protected from contaminants like arsenic.

Filtration System: Reverse osmosis
How It Works: Reverse-osmosis filters use a special membrane to remove contaminants. They're the right choice for well water that is prone to arsenic contamination.
Facts
Pros: Effective for arsenic contamination.
Cons: Requires professional installation; works very slowly; pre-and post-filters and membrane require periodic changing.
Where to Buy: GE SmartWater Reverse Osmosis filter, $299, plus about $300 for installation; www.geappliances.com. Replacement filters: $41. Replacement membrane: $99.

Problem: We have hard-water stains around our faucets and fixtures. I want to remove those metal deposits from all our water.

Filtration System: Point of entry
How It Works: Point-of-entry filtration systems hook up where the water line enters a home, filtering water for cooking, cleaning, and bathing. Good for homes with hard water.
Facts
Pros: Filters all water entering your home; protects appliances.
Cons: Professional installation required; some brands need a filter change every three months.
Where to Buy: Culligan Valve-in-Head Whole House Water Filter, $35, plus about $200 for installation; www.sears.com. Replacement filter: $7.