Choosing a water filter: Know your water and your options

Even crystal-clear, odour-free, good-tasting tap water can be hazardous to your health. Bottled water may be not be any more safe, experts say. The answer? A water filter. Read on to find out which one best fits your needs.

Some filters are great at removing lead, while others are better at ousting disease-causing microbes. The key is to know which one you need.

Home water filters range from pitchers fitted with activated-carbon "strainers" to whole-house systems. Studies show that most are quite effective. However, no filter system is capable of removing every contaminant, off taste and unpleasant odour from tap water.

Knowing what's in your water is a must in order to choose a filter that can get it out.

Local water-treatment authorities often make annual reports on water quality available to their customers. But if you have a private well or can't get a free report, you may have to pay for a water test by a private company.

Knowing your options: Types of systems

How they work: Positively charged, highly absorbent carbon in the filter attracts and traps many impurities.

Type of system: Pitchers, water bottles with filter inserts, faucet attachments, countertop and under-sink units.

What it removes: Bad tastes and odours, including chlorine.

Some also reduce contaminants such as heavy metals (copper, lead and mercury), parasites (giardia and cryptosporidium), pesticides, radon and volatile organic chemicals (methyl-tert-butyl ether, or MTBE, and dichlorobenzene and trichloroethylene, or TCE).

Disadvantage: Bacteria can grow on these filters overnight, even on "bacteriostatic" types that claim to resist bacterial growth.

Be sure to follow the manufacturer's directions for flushing the filter regularly.

How they work: Water passes through a resin bed, which removes certain minerals.

Type of system: Whole-house unit that cleans water before it's sent to faucets throughout your home.

What they remove: Nitrates, nitrites, fluorides, sulfates and bicarbonates.

Disadvantage: Water may taste salty.

How they work: "Softens" hard water by swapping minerals with a strong positive charge for ones with a lower charge.

Type of system: Whole-house unit.

What they remove: Calcium and magnesium, which form deposits in plumbing and fixtures, plus barium.

How they work: Water is heated to the boiling point and vapour is collected as it condenses.

Type of system: Whole-house unit.

What they remove: Disease-causing microorganisms, heavy metals and most chemicals (volatile organic chemicals such as gasoline, as well as radon, may remain in drinking water).

Disadvantages: Gives water a bland taste because it removes many minerals.

How it works: A semi-permeable membrane separates impurities from water.

Type of system: Under-sink units as well as whole-house system.

What it removes: Pesticides; heavy metals such as cadmium, copper, lead and mercury; and other pollutants, including arsenic, barium, nitrates/nitrites, perchlorate and selenium.

Disadvantage: Uses lots of water, and only 10 to 30 percent is released as treated drinkable water; won't remove microbes.