Reverse Osmosis Systems near you

Water from the cold line first passes through prefilters, usually a sediment stage and activated carbon, which catch particles and take out the chlorine that would otherwise attack many membranes. It then reaches the membrane under household water pressure: water molecules pass through, while most dissolved salts, metals and other substances are held back and carried away in a continuous stream to the drain.

Treated water collects slowly in the storage tank, since the membrane produces it a little at a time, and a final carbon postfilter polishes the taste on its way to the faucet. Some units skip the tank and use a pump to make water on demand, which calls for an outlet under the sink installed by an electrician if none exists. Low incoming pressure or very cold water slows production, which is why homes on a well with a low pressure setting sometimes need a booster pump.

Reverse osmosis units are certified to NSF/ANSI Standard 58. Health Canada's well water guidance lists what such devices treat: protozoa, nitrate, nitrite, pentavalent arsenic, manganese, lead and copper. Bacteria and viruses are not on that list. The same guidance adds two caveats: these systems remove only pentavalent arsenic, known as arsenic V, so the lab should confirm which form is in your water, and although reverse osmosis is effective against manganese, certified devices for it may not yet be available.

A certification covers the contaminants named in the product's listing, not everything the membrane might happen to catch, so match the claims on its performance data sheet to your test results. Health Canada strongly recommends buying a device certified to the applicable standard by a certification body the Standards Council of Canada has authorized, and notes that a certified device does not add anything harmful to the water. Look for the certification mark and a statement that the device conforms.

Reverse osmosis earns its upkeep when a test shows something it is certified to reduce. On city water, read the municipality's water quality report and, in an older home, test for lead; on a well, have an accredited laboratory check for bacteria, nitrate and the substances common in your area, as Health Canada recommends. The results tell you whether reverse osmosis is the right tool, whether a simpler filter would do, or whether the well needs repair and disinfection first.

Reverse osmosis works by rinsing away what the membrane holds back, so some water goes to the drain for every glass that reaches the faucet. How much depends on the membrane, the incoming pressure and temperature, and the design of the unit. Ask for the manufacturer's stated ratio rather than a sales estimate, and compare units on it if you pay for water by the meter or draw it from a low-yield well.

A few features keep the waste down: a shut-off valve that stops the flow once the tank is full, a permeate pump or booster where pressure is low, and prefilters changed on time so the membrane isn't working against a clog. Hearing water trickle into the drain while the tank refills is normal; a flow that never stops once the tank is full points to a failed shut-off valve. The drain line should discharge through an air gap, often built into the faucet, so wastewater can't be siphoned back toward the unit.

Because the membrane removes calcium and magnesium along with everything else, reverse osmosis water can taste flat to some people. Health Canada's position is that a reasonably balanced diet makes a mineral supplement unnecessary, so adding minerals back is about taste rather than health.

A remineralization cartridge placed after the membrane dissolves a small amount of minerals back into the water and raises its pH a little, which many people find more pleasant to drink. It adds one more cartridge to the maintenance schedule, and it changes the configuration of the unit, so check that the model you buy, with that cartridge, is the one shown in the certification listing.

The unit needs room in the sink cabinet for the filter housings and the tank, a cold-water connection, a drain connection above the trap and a hole for its faucet. Drilling a stone or quartz counter takes the right bit and some care, and a line can also be run to a refrigerator's water dispenser or ice maker if the fridge is close enough. On a well, the water should arrive free of sediment, and iron or heavy hardness can foul the membrane quickly unless it is treated upstream.

Hookups to the supply line and the drain are plumbing work: in Quebec they belong with a contractor holding the appropriate RBQ licence, and in other provinces with an installer who meets the provincial rules. Ask the installer to leave the certification listing, the performance data sheet and the maintenance schedule with you.