Reverse Osmosis FAQ



What is reverse osmosis?

Reverse osmosis, often referred to as RO, is an advanced water purification method that was initially developed by the U.S. Navy to produce drinking water from sea water for submarine crews.

It is a membrane filtration technology that works by forcing water under pressure through the very tiny pores of a semi-permeable membrane. Modern reverse osmosis units for the home combine membrane technology with carbon and mechanical filtration to produce highly purified, great-tasting water.

How does it work?

In modern home units water, driven by normal city water pressure, flows first through a carbon pre-filter, which removes organic contaminants including chlorine and its by-products.

Next, it enters the reverse osmosis membrane, a very tight, sheet-like filter, that allows water to pass but rejects dissolved solids like sodium and impurities like lead and arsenic. Some of the water entering the unit is used to cleanse the membrane surface and flows to the the kitchen drain pipes.

The purified water is stored in a small storage tank until it is needed. When the ledge faucet mounted on the sink is opened, the purified water is forced by air pressure through another carbon filter, which gives it a final polish and from there to the ledge faucet.

(This is a simplified description of a three-stage RO unit. Additional stages like sediment filters and additional carbon filters can be included. The simplified description omits a few very essential parts like flow control devices, check valves, and an automatic shutoff devices that stops the inflow of water when the storage tank is full.)

Is a reverse osmosis unit like a distiller?

Both effectively reduce “dissolved solids” content of water, but the processes are quite different.

RO filters water through a very tight semi-permeable membrane. A distiller is like a big tea kettle: it boils water, catches the steam, condenses it, and captures the resulting water. Most impurities are left behind in the boiling chamber.

Both distillers and reverse osmosis systems rely heavily on carbon filtration for chemical removal. (Cheap distillers often have little or no carbon filtration and are, therefore, of limited effectiveness.)

But isn't distilled water purer than reverse osmosis water?

Distillers typically remove a few parts per million more of common mineral constituents like sodium.

However, distillers don't do a good job with volatile chemicals with a low boiling point. Chloramines, for example, which many cities now use instead of chlorine as a disinfectant, aren't removed well by distillers.

Reverse osmosis, with the carbon filters that accompany it, does a very good job with chloramines. Unless volatile chemicals like chlorine are removed by carbon filtration before they enter the distiller, they will be released into the room air or they will end up in the distilled water.

But in general, distilled water is very pure, as is reverse osmosis water.

A guy told me reverse osmosis units waste a lot of water… Is that true?

It depends on what you mean by waste.

A home RO unit uses water to clean itself and wash away impurities. It's like a lot of other water-using appliances. We use water to wash clothes, to wash dishes, to wash cars, to flush toilets.

A reverse osmosis unit uses more water in its operation than you actually consume, but it doesn't use enough that you'll notice it on your water bill. It uses water only while it's filling its storage tank. When the tank is full, the whole unit shuts down and no water runs to drain.

In terms of expense, it's like a couple or three extra toilet flushes a day.

Can I hook the reverse osmosis unit to my refrigerator/icemaker?

Yes, if you can reach it with a ¼" tube from the undersink RO unit. We'll provide everything you need without cost if you'll let us know you need it.

Pressure is a consideration with some refrigerators, so it's a good idea to check with the manufacturer. The pressure you'll get from the RO unit is about ⅔ of the incoming line pressure.

How long will a reverse osmosis unit last?

Virtually forever if you service it regularly and replace parts that wear out, like the storage tank and the ledge faucet.

Typical membrane life is about 3 to 5 years, depending on the nature of the water that it's processing.

Some Reverse Osmosis units make 75 gallons of water a day, but some only make 12 or 16, yet the cost is about the same. — Why would anyone buy the low producing RO unit?

More isn't always better. If you need 75 gallons a day, then you should buy the bigger unit. But if you're only going to use 3 gallons per day, a lower production membrane will probably last longer and do a better job because it gets to run longer and spends less time sitting idle.

Reverse osmosis membranes clean themselves as they process water, so it's really healthier if the membrane has to work longer to fill the tank.

Think of it this way: If you draw off a gallon of water, a 24-gallon-per-day membrane will refill the tank at the rate of about a gallon per hour. For most users, that's plenty fast.

A guy who sells filters showed me a chart that said reverse osmosis doesn't remove chlorine. Is that true?

That guy may someday be president, because technically what he said was true, but for practical purposes it's an out-and-out lie.

It's true that the reverse osmosis membrane doesn't remove chlorine. It doesn't have to, because it has a couple of high quality carbon filters with it that do the job. In fact, if the first carbon filter didn't remove all the chlorine, the membrane would get eaten alive in no time.

Statements like this are an obvious effort to deceive. It's surprising that some very large companies repeat such misrepresentations just to sell their products.

The same guy told me that reverse osmosis units remove minerals that are essential to health. Is that true or is he again twisting the truth?

It's true that RO units remove minerals—about 95% of the mineral content anyway—but he isn't really telling you the whole story.

The mineral issue is probably the most controversial question in drinking water purification. Experts on both sides of the issue speak convincingly.

My own view, after reading much of the expert opinion, is that the mineral content of water—either high or low—isn't nearly as important as they would have you believe. That is, minerals in water are inorganic and hard for your body to use. You get most of your minerals from food, which provides organic, easily assimilated minerals.

The human body is a sophisticated instrument capable of adapting to a wide range of circumstances and capable of thriving in areas having water of high or low mineral content. As long as water is palatable, it's within the body's acceptable range.

The main issue with water is chemicals, not minerals. Whether water contains 30 or 3 parts per million calcium isn't really significant, but the difference between 0.5 and 5 parts per million chloroform is of life or death importance.

Do reverse osmosis units need electricity?

No, they run on water pressure. You need electricity only if you add an electric pressure-boost pump or an ultraviolet lamp. Standard units have neither and normally don't need them.

Why are reverse osmosis units so popular?

Because they produce great-tasting, very pure water at a very reasonable cost and in a trouble-free, fully automatic format.

We've found that RO customers are very loyal. And the most frequent comment we get is: “We drink so much more water than we used to.”

Why do some reverse osmosis units cost $1300 and others cost $189?

Beats me. Especially the $1300 ones.

The thing about getting what you pay for is true sometimes, but not always. Often the more expensive RO units are actually inferior. Many use undersized filters in an effort to achieve a stylish appearance. And they often have some bells and whistles that are more trouble than they're worth.

The most obvious example here is the “smart faucet” that contains a light that is supposed to signal the need for membrane replacement. What you usually end up with is a mediocre faucet with an unreliable dissolved solids meter built in. Soon the light doesn't work and you have a mediocre faucet that will eventually cost $125 to replace. We prefer to give you a great faucet with a lifetime guarantee and a hand-held dissolved solids tester that gives you an accurate, digital reading of your unit's performance rather than a red or green light. (We also hope you'll test your friend Bob's water with it and tell him he need one of our RO units.)

As for the $189 unit, what you usually get is the least expensive part available, the bottom of the line, in every category. That's not to say that some of the parts aren't excellent. But using the faucet again as the example, for about $4 less wholesale than we pay for our faucets we can buy the same faucet they use with the $189 units. It lasts about a year before the handle falls off. We know. We bought some and have had to replace them all. For the $4 more that we pay for our sturdy, standard lead-free faucet, we get a faucet that we can guarantee for life and hardly ever have to replace.

Anyway, we build the best RO unit we can and sell it for the what we have to get to stay in business and try not to worry about what everyone else is doing.

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