That's right, reverse osmosis water units are hard to beat when you have a problem like salt in your drinking water supply. But most of us don't have that problem; we get our water from a municipal supplier or from a chlorinated well. And, for those people, I've got good news indeed. You will get a better result from selective filtration systems than you ever could with reverse osmosis. In today's article we will examine both systems and how they differ. Then you can decide which one is best for your situation.



A semi-permeable membrane is the work horse of these units. Water is forced against the membrane and all particles larger than a molecule of water are rejected. These pores are so very tiny it often becomes impossible for water molecules themselves to pass through and, consequently, a gallon or more of water can be thrown out, along with any filtered contaminants and minerals, for every gallon that gets through the filter.

Some people throughout the US are also dealing with excessive minerals in their water and the fact that RO systems remove these minerals is another reason people have liked them. But, too much of a good thing can be bad.

You see, it seems water with no minerals is not good. That makes sense since nowhere on earth does pure water exist naturally. We need trace minerals like calcium and potassium, for example, in order to stay healthy. And, pure H2O is slightly acidic, so, when we drink this water it will try to get back to a neutral state by stealing minerals such as calcium from our teeth, bones or cells. In this case it produces calcium carbonate as its neutralizing element.

Health experts also tell us that cancer cells seem to grow only in a slightly acidic environment and, for that reason, they feels there is a long-term health risk associated with drinking demineralized water.

Reverse osmosis will not remove contaminants such as drugs, chlorine, THMs (chlorine byproducts-carcenogens), herbicides, pesticides, SOCs, etc. because molecules are very small and will pass through the membrane. The EPA recognizes activated charcoal as the best filter for removing these compounds and you must be certain you have one if you go the RO route.

Since the pores in the membrane are so tiny, you must have sufficient water pressure to force the water through the system and this may necessitate a booster pump be added.

If you want to have more than just drinking water from an RO system you will need to add a storage tank, since these systems only filter a gallon or so of water per hour. In order to keep a constant pressure on the system a tank with a diaphragm is normally used.

All in all, they are bulky units, what with the filter, a storage tank, and, maybe, an extra pump. All of this often means more expense, usually requires a plumber to install, and leads to extra maintenance cost somewhere down the line.

Anymore, I feel like using a RO system where you could have used selective filtration is like hunting flies with a cannon...they're clunky, expensive and give a dangerous result.

Selective filtration is also called multi-stage filtration and it is a good alternative to reverse osmosis.

These systems also use activated carbon to clean up any drugs or chemicals that might be in the water, but this carbon is first blended with a chemically charged resin and compressed into a solid block composed of tiny, submicron pores.

One cubic foot of this activated charcoal that has been so tightly compressed has the adsorption area of five square miles, according to scientists. The tiny pores filter out tiny, chlorine-resistant, cysts like Cryptosporidium and Guardia and the rest of the surface area scrubs up the chemicals and drugs.

What about the filter resin that covers the surface of the adsorption area?

As water passes across the resin, positively charged heavy mineral ions in the water, like lead or mercury, for example, are forced to break their bonds with water, and attach to the chemically charged resin like little magnets. Lighter minerals like calcium and potassium stay put.

The systems are very compact and uncomplicated looking. They clean the water and leave the good minerals, and they are very quick, so complicated storage tanks, booster pumps, operating electricity, etc. are not needed. And, without all that "stuff", if they are hooked up right, they produce a steady source of good water with very little maintenance.

If you have a really gross water condition to remedy, it is always wise to talk to a technical representative for any filter system you are considering. These techs are great and they almost always have a solution. And, please note, selective filtration is not designed to treat brackish or salty water.