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Reverse Osmosis Water Filter
Reverse osmosis (RO) is kind of an exotic name for water filtering—why does it get so much attention? One reason is that the reverse osmosis water filter uses technology once available pretty much only for converting salt water to fresh water on military ships, and allows us to obtain extremely clean and fresh water at a fairly modest price.
Originally developed in the 1950s, we began seeing very expensive RO systems for residential use a couple of decades later. As the industry has developed, refinements in methods and reverse osmosis water filter membrane materials have improved the life and reduced the costs.
But the defining feature is that you get water that is much cleaner water than what comes from a conventional water filter. Not everybody needs or wants to pay for such water quality, but it clearly meets the need of many consumers.
A Brief Explanation. We’re all familiar with the idea of running a liquid through a simple filter or sieve to remove unwanted items, whether in the kitchen or in the garage. The finer the gaps in the filter cloth the smaller the junk you can remove. If the holes are too small, it can take forever to run the sauce through the cheesecloth. But if you could somehow use pressure to force the liquid through the filter that would improve performance. In fact, it would let you use a filter, or membrane, with much smaller holes.
A reverse osmosis water filter uses a membrane with outrageously small openings, whereby the only way to get the water molecules to pass is to do it under pressure. How small are the membrane openings, or pores? It’s hard to explain how small they are—would you believe 0.00000004 inches? That is thousands of times smaller than the pore size of the typical water filter, and is why you can literally turn salt water into fresh water.
To create the pressurized environment, the membrane is within a steel container with the higher pressure on one side of it and the outlet, at lower pressure on the other side. The pressure forces the water through the pores, leaving the bad stuff behind. Newer versions have clever ways of flushing most of the accumulated bad stuff away, to be dumped down the drain (remember, it would be in that drain water anyway if you were not using the reverse osmosis water filter system). This extends the life of the filter membrane, thus reducing the average cost per gallon (which can run around $0.20 per gallon; it’s affordable but you won’t want to flush your toilet with such “nice” water). By the way, a Ro unit usually includes a conventional cartridge filter before the membrane, to remove the easy stuff first and use the heavy artillery for the harder-to-remove substances.
What Does RO remove? The scientists can give you a long list of evil substances, like copper sulfate (removes around 99% of this); radioactivity (Really?! removes 95% to 99% of this, which fortunately is usually in small doses to begin with); lead (95% to 99%) mercury (same percentages); DDT (99.9% thankfully) and dozens of other materials. In short, a reverse osmosis water filter system takes out chlorine, pesticides, bacteria, viruses and many chemical contaminants. If you need really clean water, RO is the method for you.
Other Considerations. Water filtered by RO is pretty affordable, but 20 cents per gallon (or thereabouts depending on a bunch of factors) is considerably more expensive than conventionally filtered water, which could run closer to a penny a gallon. If your water supply is pretty good, with a minimum of dangerous viruses or kryptonite, and if health issues are not a problem, consider going with one of the filtering systems discussed elsewhere on this website. If you do want to go with a reverse osmosis water filter system, you may want to add it under the sink in the kitchen, for drinking and cooking. If you put it in the main house line and run through say 100 gallons per day (easy; much more for some families) that could be $20 per day, and you’d need a big system to handle the volume requirements. So a smaller system under the sink would be a good compromise. If you or a family member do have health issues, you could add a RO unit in all of the bathrooms where water is consumed orally.
Don’t go for the cheapest system. These are pressurized vessels and we are dealing with some technology here; you don’t want to by a cheap plastic container or the least expensive membrane system. In simple terms, you probably won’t be happy with a system that cost less than around $200 to $250 unless that price represents a killer discount. Also, find out about the membrane itself; you don’t want to be changing the membrane every year or two ( a good one should run 5 years or more). Similarly, the pre-filter element should be able to go upwards of a year before replacement, vs. maybe 4-6 months for cheaper/smaller filters. You’d like to be able to replace filters yourself if possible.
In conclusion, a reverse osmosis water filter system is an affordable way to achieve extremely clean water, but it is not for everyone. It is an investment you’ll appreciate for many years, so it is worth a bit of time up-front to understand the features, quality and cost of the most popular brands on the market. Virtually all of the major manufacturers sell systems online, and many can put you in touch with a local contractor for installation and service.