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Reverse osmosis produces water of remarkable purity by separating chemicals, pesticides, pharmaceuticals, and dissolved solids from the water. While rarely used as a whole house water filtration system, some groundwater is so severely contaminated reverse osmosis is the only viable option for providing the home with clean water. A whole house reverse osmosis system requires careful planning, diligent maintenance, and a researched understanding of your water’s chemistry. Whole house reverse osmosis systems can be complex endeavors, but they can also restore water quality to homes affected by astronomical levels of TDS or dangerous quantities of contaminants like hexavalent chromium.

What is a whole house reverse osmosis system? 

A whole house reverse osmosis system is a water filtration system that filters the entirety of your home’s water through a reverse osmosis membrane. A whole house reverse osmosis system is installed at the point where water enters your home. Every drop of water entering your household plumbing is treated by the reverse osmosis membrane, from your drinking water at your kitchen sink to the water you use to shave, shower, and flush your toilets. Whole house reverse osmosis (RO) systems ensure that your entire home is free from any traces of water hardness, salts, chemicals, and TDS. The microscopic pores on the semipermeable membrane of the RO system can eliminate over 98% of dissolved organic and inorganic matter. The water produced by reverse osmosis is almost unparalleled in its purity, and it is a more cost-effective method of purification compared to deionization or distillation. While reverse osmosis is commonly used for residential point-of-use drinking water, those with extremely challenging water conditions install a whole house RO system to provide them exceptional water quality throughout their home. 

Reverse osmosis removes a host of contaminants, like chromium, uranium, copper, mercury, arsenic, boron, silver, lead, sodium, and nitrates. Many of these can pose health risks in elevated quantities, and there are limited filtration methods effective at eliminating these all at once. While an under-sink RO system is ideal for providing purified water at a single faucet, sometimes water presents challenges that can affect your whole home. If your water source is compromised by toxic levels of chemicals and metals, it can be wise to eliminate these from every faucet in your home. There are some cases where water you brush your teeth with, bathe your children in, and use to cook and clean should all be purified by reverse osmosis.  

Learn more about how reverse osmosis works. | Learn more about the stages of reverse osmosis.

Is a whole house reverse osmosis system necessary? 

A whole house reverse osmosis system is only necessary for very specific water problems. There are very few water quality issues that are so severe they can only be addressed by whole house reverse osmosis. Whole house reverse osmosis will most commonly be found in rural homes on wells, where the groundwater is compromised by numerous difficult contaminants. Water with high levels of naturally occurring compounds like arsenic and nitrates can only be treated by reverse osmosis.  Homes built near manufacturing plants may see elevated levels of microplastics, volatile organic compounds like benzene, chemicals like PFAS, or high concentrations of dissolved salts. Removing these contaminants poses a unique challenge that few water filtration systems are equipped to tackle. When these contaminants emerge in unison they can be especially troublesome, and reverse osmosis is sometimes the most viable way to eliminate them from the water. If you live with water with exceptionally elevated levels of TDS, you may decide you want to protect your entire home from these contaminants by installing a whole house RO system. 

Municipal water supplies are disinfected by chlorination and quite unlikely to contain levels of contaminants that could only be addressed by reverse osmosis. Contaminants you may find in city water like water hardness, chlorine, chloramines, and lead can all be treated effectively by other whole house water filtration systems. However, some people on municipal water simply prefer RO water and want the entirety of their home to use reverse osmosis water. People are also increasingly concerned about the presence of fluoride in municipal water. Fluoride, a naturally occurring mineral, is synthetically added to city water supplies to reduce the risk of tooth decay in children. Fluoride is extremely tough to remove from water. The industry standard for removing it is by using a filtration media called activated alumina, a process that is impractical for most applications. Activated alumina requires very lengthy contact time with the water to reduce fluoride, and produces water at a rate of about 0.25 GPM. Plumbing a whole house with such low water pressure is ultimately unfeasible, so those wanting to remove fluoride from their home entirely usually turn to reverse osmosis. 

how reverse osmosis works

How do I know if I need whole house reverse osmosis? 

The only way to truly know if your water needs to be treated by whole house reverse osmosis is to perform a detailed water test. Many contaminants that pose the biggest threat to your health and your home are tasteless, odorless, and colorless. Your well water may be discolored, taste like metal, and bear a harsh odor, but many of these problems are solvable by much simpler filtration systems. A rigorous water test kit will reveal your water’s organic, chemical, and metallic composition, identifying the levels of everything from pesticides and ammonia to arsenic and cyanide. Without a thorough understanding of what is in your water, it is impossible to know how to best go about eliminating the contaminants. A water test will help illuminate what pretreatment your water needs to undergo before it reaches the reverse osmosis system. Without a water test, you will also be unable to gauge the success of your whole house reverse osmosis system. 

If the water test reveals your well has concentrations of nitrates, nitrites, arsenic, chromium, or TDS far above what the EPA has established as safe, you then need to contact a water specialist. While an under-sink reverse osmosis system can be used to restore your drinking water’s taste and safety, there are some applications where you will need a system to service the entirety of your home. 

How do I test my well water? 

The best way to test your well water is to collect a water sample from your well and send it to a state or nationally certified laboratory to be tested. Your water samples will then be subjected to the same water quality tests used to ensure the safety of bottled water and municipal water supplies. Water test labs use the EPA standards for safe drinking water to check your well, measuring the presence of contaminants in the parts-per-million. Within two weeks, they will return your report to you, flagging every instance where your water exceeds the EPA’s regulatory standards for safe drinking water. 

Since private wells are unregulated, it is incumbent upon the well owner to test their water and ensure their home’s drinking water is safe. If you are on a well, performing detailed water tests should be an annual part of your diligent well maintenance. Furthermore, if you are considering a whole house reverse osmosis system, it’s necessary to understand exactly what is present in your water so you can craft an effective strategy for achieving the high-purity water you desire. If you are on municipal water, you have the option of performing a lab test. However, cities are mandated by the EPA to release an annual water quality report. The Environmental Working Group (EWG) maintains an online database of these reports, which are searchable by zip code. 

Learn more about how to remove bacteria from well water.

What to consider before installing a whole house reverse osmosis system 

A whole house reverse osmosis system requires significant planning, dedication, and maintenance for it to produce the desired results. A point-of-use RO system in your kitchen only needs a single connection to your plumbing, a dedicated air gap faucet, and one or two storage tanks. A whole house system requires much more consideration. You will need to factor in what pretreatment is necessary to protect the RO membrane, how many gallons per day your household will use, and the space required to house the system. 

1. Pretreatment of the water

Very few whole house reverse osmosis systems exist in isolation. If the water quality from your well is so poor that you need a whole house system, it’s likely you will need the aid of other water treatment systems to preserve the RO system and maximize performance. The reverse osmosis membrane is adept at eliminating chemicals, salts, and dissolved inorganic matter. However, to prolong the lifespan of the membrane, it needs to be protected from certain water contaminants. This is one of the many reasons why a thorough water test is necessary, as knowing the composition of your water informs how best to pre-treat it. 

If you have very hard water, the water hardness minerals will wreak havoc on the membrane. Calcium and magnesium, the minerals that make water hard, are notorious for creating scale build-ups on appliances, water heaters, and inside of plumbing. These minerals will have a similar destructive impact on the RO membrane. The minerals will collect within the membrane, binding, hardening, and calcifying into a scaly blockage. This causes both the output of the membrane to decrease and the quality of the membrane’s output to decline. Ultimately, the membrane will fail. Membranes treating hard water will require frequent replacements, far sooner than the manufacturer’s recommendation. If you are going to install a whole-house RO system and you are on hard water, it is wise to install a water softener before the system. Water softeners will eliminate calcium and magnesium from the water, preserving your RO’s efficiency and the longevity of your membrane. 

Similarly, if your well water is very high in iron, you will need to use an ion exchange water softener or iron filter to eliminate the metal from your water. Iron can cause the RO membrane to foul, impeding its ability to reject dissolved solids and diminishing the amount of pure water it can produce in a day. 

Almost all RO systems require both sediment and carbon prefilters. Sediment filters act as a mechanical screen, sieving grit, sand, and debris out of the water. The membrane is capable of eliminating sediment on its own, but large quantities of sediment would quickly clog the membrane. More importantly, though the membrane is capable of rejecting any particulate matter in your water, all the wastewater generated by the reverse osmosis unit drains through a tiny flow restrictor. This flow restrictor would quickly become clogged if dirt and debris were flushed through it along with the rejected dissolved inorganic contaminants. Since the flow restrictor pressurizes the reverse osmosis membrane as well as balances the recovery ratio of the system, it is important to keep it clear and free from sediment.

Reverse osmosis systems employ carbon filters to eliminate chlorine from the water before it reaches the membrane. Thin film composite and thin film material (TFC and TFM) membranes are unable to tolerate any degree of chlorine, so carbon filtration is employed to protect the membrane from contact with chlorine. Carbon eliminates chlorine through a process called adsorption. Chlorine and organic compounds (like VOCs) adhere to the carbon’s expansive, porous surface area. 

Explore how water softeners work. | Learn more about how sediment filters work

2. Sizing the whole house RO system

Perhaps the most important thing when selecting a whole-house RO system is making sure you find one that can support your daily water usage. Generally speaking, each member of the household will use between 60-75 gallons of water per day. However, this number varies. A household with young children will tend to use more water, while a home with working adults may use less. Regardless, you need to make sure you select a system with an output high enough to support each individual’s water use and choose a tank that can store enough water to service every member of the family throughout the day.  

For example, a house of four would want to have access to at least a 250 gallon storage tank. Part of the key to running a successful whole house reverse osmosis system is ensuring that you have a system with a great enough output to keep the tank full. The reverse osmosis process works very slowly, with many residential under-sink units only producing around 50 gallons per day. To plumb a whole house, you want a system that will be able to replenish your storage tank without you ever running out of water. So, for a family of four using a 250 gallon storage tank, something like a 1,000 GPD RO system may be ideal. A 1,000 GPD system operating at peak capacity would take a little over 6 hours to fill up a 250 gallon tank. (As a 1,000 GPD system would be producing between 41-42 gallons of water an hour.) If the RO’s output is too low, the tank will never become full, and the RO unit will be running constantly to barely meet the household water demands. If you were ever to host family or friends for an overnight stay or large dinner party, the tank would empty out rapidly and be unable to catch up to demands exerted on it by the guests. This is why you would need a system capable of producing something like a 1,000 gallons per day, even if you plan on using less than half that. Whenever you are sizing a whole house reverse osmosis system, you should call a water specialist and have them help you correctly size the system and tank to support you and your home. 

Learn more about how water storage tanks work. | Learn how reverse osmosis tanks work.

3. Post-treatment of the water

Your water needs to be pretreated to protect the RO’s membrane and promote peak efficiency of your system. However, the water also needs to be treated after exiting the tank and before entering your house. Most whole house RO systems will be followed by a pH adjuster (also known as an acid neutralizer). RO water is mildly acidic, usually falling between 5-6 pH. Acidic water is corrosive, eroding copper plumbing and causing pinhole leaks to sprout. Many under-sink reverse osmosis systems include a remineralizer cartridge to add mineral content back into the water and buffer the pH. However, a whole house RO system is processing a much greater volume of water. A small inline cartridge would not bear much influence on the water’s pH and would significantly reduce water pressure. Passing through water through calcite, a calcium-rich crushed marble media high in alkalinity, will boost the water’s pH and protect your plumbing from damage. 

Most whole house reverse osmosis systems are also followed by a UV purification system. If you are on well water dire enough to require whole house reverse osmosis, it’s very likely there is potentially harmful bacteria or microorganisms present in your water supply. UV systems neutralize the DNA of pathogenic bacteria by dosing them with germicidal UV-C light. While reverse osmosis is adept at eliminating a host of dissolved contaminants, it should never be used for microbiological disinfection. Living organisms and viruses should always be removed by UV. Furthermore, there is always the possibility for bacteria to grow within the membrane or in the storage tank. Living organisms and viruses should always be removed by UV. This is why ultraviolet purification is always recommended as the final stage in a whole house filtration system. 

Learn more about how UV purification works. | Read about how to treat acidic water

4. Space to hold the whole house RO system

Whole house reverse osmosis systems take up a lot of space. As we’ve discussed, you will need substantial prefiltration and post-treatment of the water to ensure the reverse osmosis membrane operates effectively. You will need a spacious room to install water softeners and their brine tanks, a mineral tank for your pH adjuster, and the large RO system itself. Water storage tanks capable of holding 250-500 gallons of water are going to be six feet tall or greater. 

Since it’s necessary to install a reverse osmosis system indoors and in a room where temperatures won’t cause the water or equipment to freeze, you may need to renovate your basement or a spare room of the house to comfortably hold all of this equipment. You also want to make sure you have plenty of space for filter changes, system maintenance, and installation. You don’t want to climb through a jungle gym of plumbing and filtration equipment to refill the resin in your softener or flush out your spin-down sediment filter. You also need to choose a room in your home where you can easily plumb your water main from your well. Since reverse osmosis systems do drain wastewater (as do water softeners), you’ll also want to select a location where the systems can drain without risking backflow. 

Also, consider that household water supplies will demand pressurized water. Not only are you running water to your tap and your refrigerator, but you’ll need enough water pressure to run baths and flush toilets. To achieve this, you will need to install a water booster pump as well. Grundfos pumps are high performance, energy-efficient pumps that can boost the water pressure of your water storage tank and are commonly used in both commercial and residential applications, like whole house reverse osmosis. When choosing a pump, consider how far the water needs to be transported from the tank. The further the water needs to travel, the greater the likelihood flow rates will decrease. For example, if you are running plumbing to an upstairs bathroom, you will need to choose a pump capable of generating enough pressure to keep the shower from running at a slow trickle. The booster pump will also need to be installed in-line with your plumbing, after the RO system and post-treatment and before the water enters your home. 

Explore how water booster pumps work. |  Learn how to troubleshoot your reverse osmosis system

5. Waste 

Reverse osmosis systems generate wastewater as a byproduct of their water purification systems. Design and technological innovations continue to find ways to eliminate the inefficiency of reverse osmosis, but there is no way to create RO water without wasting water. The purified water (called permeate) is physically separated from the solution brimming with contaminants (called the brine) by the membrane. The brine is then flushed out of the system and down a dedicated drain. Larger, commercial systems have become especially adept at lowering the rate of rejected water, but these systems are also handling much greater volumes of water. To use the example from before, say you had a 1,000 GPD whole house RO system and a 250 gallon tank operating at 1:1 efficiency (for every gallon of permeate produced, only one gallon of brine was sent to the drain.) It would require 500 gallons of water to fill that tank to the top with purified RO water. 

If you have a lower efficiency system, you could potentially send up to thousands of gallons to the drain every day. Even in high-efficiency systems, waste and recovery will be influenced by your raw water chemistry. As water scarcity continues to spread across the American Midwest, having your home dependent on such a high waste system can be a cause for concern.

| Learn more about how a permeate pump can reduce waste in reverse osmosis. |

How much does a whole house reverse osmosis system cost? 

A whole house reverse osmosis system will cost around $12,000 to $20,000. While the price of a commercial-grade reverse osmosis system is around $3,000-$5,000, the pretreatment of the water, the pressure booster pumps, and the installation will all increase the cost. The RO’s filters and membranes require regular replacements, as will the components of your other filtration systems. Water softeners require resin beads and periodic replenishment of salt in the brine tank. UV lamps need to be changed every year, and the quartz sleeves every two years. Carbon and sediment filters usually need to be changed every six months, and your acid neutralizer will dissolve its calcite media over time. 

The cost of whole house reverse osmosis also heavily depends on the size and output of the system. The greater the gallons per day produced by the system, the more expensive the initial cost will be. A higher output system demands a larger storage tank, which is another expense to factor in to the overall cost. Though you can install the system yourself, it is wise to consult a professional plumber or water treatment expert. Whole house RO is complex and it is vital that all the components are installed properly. Otherwise, you could see diminished household pressure and flow rates and risk reduced performance from your system. Whole house reverse osmosis is an expensive investment with ongoing costs and regular maintenance. However, in situations where it is the only option to purify your water, it can be a welcome relief from hazardous water quality.


4 comments

  • My well water has 600mg/l chloride, 185 Sodium. I’ve been on this well 15 years have under the counter R/O for drinking water. I’m replacing the water softener do I need a whole house R/O? Other than the chloride and hard water no other problems in the water.

    Gregg on

  • Will the whole house/shower heads, faucets, etc., then need to have special RO compatible faucets? I can’t seem to find anything other than single cold water faucets.

    Katherine Julia on

  • Dear Cheryl,

    Yes. Both reactive silica and colloidal silica can be removed by the reverse osmosis membrane. RO can usually reject around 90-98% of silica from the water. Reverse osmosis is generally recommended when the reactive silica is around or below 20ppm (usually found in surface waters or shallow wells). If you have higher levels of silica, like 50+ppm, reverse osmosis is a less effective filtration method, as the silica can foul the RO membrane.

    John Woodard, Master Water Specialist on

  • question, can you tell me if Silica (reactive form) can be removed by RO?

    Cheryl on

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