A whole house reverse osmosis system sends all the water entering your home through a reverse osmosis (RO) membrane, not just the water at the kitchen tap. It is a big installation with real running costs. Our honest view is that most Durham Region homes do not need one, but a few rural wells are a different story. Here is what it involves and how to tell which camp you are in.
Point of entry versus point of use
A point-of-use system treats water at a single tap. A point-of-entry system, also called a whole-home system, treats everything coming into the house. Health Canada suggests working out which one you need before you choose, and buying a device certified to the right NSF/ANSI standard for your problem.
Most home RO is point-of-use: an under-sink unit in the kitchen cabinet feeding one faucet for drinking and cooking. Health Canada's drinking water guidance puts it plainly. Certified RO systems "are intended for point-of-use installation only." A whole-house setup needs much more incoming water to make enough treated water, and RO-treated water may be corrosive to the plumbing inside your home.
The trade-offs
Reject water
An RO membrane splits incoming water into two streams: treated water, and a concentrate that carries away what the membrane held back. The U.S. EPA's WaterSense program says a typical under-sink RO system sends five or more litres down the drain for every litre of treated water. Models that earn its label must send 2.3 litres or less. Whole-house recovery rates depend on the equipment and your water, so ask for the rated figure in writing. The volume adds up fast when the system is treating your showers and laundry as well.
On municipal water, that extra water runs through your meter. On a private well, the well has to supply it, and on a septic system the concentrate adds to what the septic has to handle. Ontario's SepticSmart guide tells rural owners to conserve water to cut the wastewater their system must treat, and not to send softener backwash into it unless the system was designed for that. Find out where the concentrate would drain before you go further.
Storage tank and repressurizing pump
A membrane makes water slowly. On its own it could not supply a shower and a washing machine at the same time. So a whole-house system fills a storage tank, and a repressurizing pump sends that water back out to the house at normal pressure, as one manufacturer's spec page explains. Some designs also use a high-pressure pump to push water through the membrane. Pumps need electricity, so ask how you get water if a pump fails or the power goes out.
Pre-treatment
Hard water, iron and chlorine all shorten membrane life. The Region of Durham's Private Well Water Manual says hard water may plug RO membranes and that RO needs pre-filtration and pre-softening of hard water. Chlorine is the other problem. DuPont's FilmTec technical manual allows a maximum of 0.1 mg/L of free chlorine and recommends removing it before the membrane. Durham disinfects its municipal water with chlorine, so city homes would need a carbon stage too. In practice, a whole house reverse osmosis system sits behind a softener, an iron filter if the water needs one, and sediment and carbon filters.
Low-mineral water and your pipes
RO strips out most dissolved minerals, and water without them behaves differently in your plumbing. Health Canada's corrosion guidance notes that lead and copper levels at the tap usually rise when alkalinity is low, and fall as pH goes up. That is why whole-house designs often add a remineralizing or pH-correction stage after the membrane to put some calcium and magnesium back. Health Canada also recommends having an accredited lab test the water going into and coming out of a treatment system after installation.
Space, power and running costs
Put together, you are looking at pre-treatment, the RO unit, a storage tank, at least one pump and a remineralizer. All of it has to sit somewhere that stays above freezing, with a drain and power nearby, and it takes far more room than a filter. Running costs cover pre-filters, membranes, remineralizing media, softener salt, electricity and the extra water.
Our 2026 Oshawa plumbing cost guide puts water filtration at $300 to $800 for an under-sink system and $1,000 to $3,000 for a whole-house system. It has no figure for whole-house RO, which is a bigger installation, so any price would come after a water test.
When a whole house reverse osmosis system can be justified
Rarely, and almost always on a private well. Many homes in rural Uxbridge, Scugog and Clarington draw from wells, and the owner is responsible for the water. Start with testing. The Region of Durham tests private well water for bacteria free of charge and recommends testing at least three times a year. Chemical tests are usually done by private labs, its manual notes. Health Canada also suggests testing general water quality every two years. These include pH, iron, chloride, hardness and total dissolved solids, which can affect plumbing and treatment equipment.
Whole-house RO is worth discussing when a problem shows up at every tap and standard equipment cannot fix it. The clearest case is water loaded with dissolved salts. Health Canada's aesthetic objective for total dissolved solids is 500 mg/L or less, and above that, water causes excessive scaling in pipes, water heaters and appliances. A softener will not take out salt that is already in the water, because it swaps calcium and magnesium for sodium or potassium. Durham's well manual warns that wells near roads and parking lots can pick up road salt, and it lists RO among the treatments for high sodium and for sulphates.
Many other well problems have simpler answers. Health Canada lists certified RO (NSF/ANSI 58) for nitrate, nitrite, pentavalent arsenic, lead and copper, and certified RO is meant for a single tap. So the usual fix there is an under-sink unit where you drink and cook. Iron and hardness respond to filtration and softening. For bacteria, Durham's manual points to finding the source, shock chlorination and treatment such as UV or chlorination. RO is not on that list.
What most Durham homes need instead
Homes on the Region's Lake Ontario supply, which serves Oshawa, Whitby, Ajax, Pickering and Bowmanville among others, get water with a hardness of 125 mg/L as calcium carbonate, according to the Region of Durham. The Region says its water is safe and meets aesthetic guidelines, and that a softener or filtration system is a personal preference. It disinfects with chlorine, which some people can taste and smell.
For those homes a combination usually does the job. Whole-home carbon filtration reduces the chlorine taste and odour at every tap and shower. A softener deals with hardness if it bothers you. An under-sink RO unit at the kitchen covers drinking and cooking. You get RO water where you actually drink it, without running a tank-and-pump system for the whole house. Port Perry's municipal wells measure 274 mg/L, and Health Canada considers water above 200 mg/L poor, so a softener matters more there.
We cover whole-home filtration in why you should consider a whole house water filtration system and the basics of RO and softeners in the ABCs of reverse osmosis and water softeners. For what RO filtration removes, see our guide to reverse osmosis water filtration.
Where Hayes fits in
Hayes Plumbing sells, installs and repairs water treatment equipment for homes across Durham Region: whole-home filtration, under-sink and reverse osmosis drinking water systems, water softeners, and sediment, iron and sulphur treatment for well water. We test your water before recommending anything. If the results suggest a whole house reverse osmosis system is worth a look, we will walk you through what it would involve and how it compares with a softener, filtration and an under-sink unit. Financing and rentals are available.
Book a water test
Call (905) 576-3043 or request a visit. The office is open Monday to Friday, 8 AM to 4 PM. You can also read more about our water filtration and water softener services.