Should I Choose Reverse Osmosis?

A Reader Writes The Green Guide:

I recently purchased a reverse osmosis system, brand name Aquathin. Do you know of this company? I am frustrated with the water waste of about 4:1. I end up pouring the wastewater on my garden.

The Green Guide Responds:

Reverse osmosis (RO) is a filtration method that forces water through a semi-permeable membrane. It is perhaps the most effective form of water filtration, catching pathogens, dissolved solids and organics, heavy metals like lead and asbestos, and some (though not all) pesticides and VOCs. But there are problems: for every gallon of water filtered, from three to nine gallons are used, depending on your system. That's a lot of water—perhaps useful if you have a garden, wasteful if you don't. Furthermore, RO can take up to four hours per gallon, so you have to think ahead. And it's expensive, compared with other filtration methods.

Aquathin, combines the two most effective methods of water filtration—reverse osmosis and activated carbon (AC) filtration—with a third, de-ionization (DI). AC combined with DI is the method used by Brita and other common filters: AC removes the organic substances that often affect taste, odor, and color, as well as chlorine, but is not generally effective on heavy metals, microbes, and nitrates; the DI ion-exchange resin acts on heavy metals. That is to say, a Brita-type AC/DI filter gets at many of the substances an RO filter does, though it doesn't necessarily reduce them as much. Further, to filter out pathogens, you need to buy an AC filter specially certified to remove cysts.

To economize, the Green Guide recommends that you get your water tested, so you can know exactly how comprehensive a filter it's worth your paying for. But expense and waste aside, a combined AC-RO filter is generally considered the most effective across the broadest range of contaminants, and Aquathin claims that its triple combination filter is better at removing heavy metals and organic contaminants than is standard AC filtration. Furthermore, Aquathin claims to totally remove viruses, cysts, and fecal coliform. Evaluating its claims is difficult, though, because of the company's approach to certification.

There are two prominent certification bodies for water filters: the National Sanitation Foundation (NSF), which gives a blue circular seal to certified products, and the Water Quality Association (WAQ), which gives a gold seal. Both organizations have searchable databases of certified products: for NSF's click here, for WAQ's click here. Aquathin president Alfred Lipshutz told the Green Guide that his company uses neither certification because they believe it "more credible to have systems tested at the site of contamination," and because both NSF and WQA test filters one contaminant at a time, instead of testing actual on-site water with multiple contaminants. Aquathin instead tests its products in EPA-certified laboratories. Documentation is available from Aquathin dealers, but not online. We'd recommend you flip through the documentation before making your purchase.