Southampton Legionella Risk Assessment Association Guide

By the time you finish reading this, you’ll understand why some home water treatment systems are better than others. Here we go: First, just a little background: There are basically two kinds of water treatment products, or home water treatment systems, widely sold in the United States: Reverse Osmosis, and Carbon Filtration. There are also steam distillation and a couple of others, but they’re not widely used because of cost and convenience considerations.If you’re looking for more tips, Southampton Legionella Risk Assessment Association has it for you.

Reverse Osmosis systems force water through a membrane with very tiny pores that are just large enough for a water molecule to pass through. Everything larger than a water molecule gets filtered out and flushed down the drain.

Home water treatment systems using carbon filtration technology trap impurities and contaminants in the tiny nooks and crannies of a block of activated carbon in two ways. A one-pound block of activated carbon can have more than 150 acres of surface area, as unbelievable as that sounds. That means that there are miles and miles of tiny passages and channels and tunnels small enough to trap contaminants.

In addition, the carbon is “activated”, meaning that it has a small positive electrical charge. Contaminants in the water have a negative charge, so they are attracted to, and held by the carbon.

Which technology is better? Here are some comparisons:


The better versions of both types will filter out chlorine, lead and other heavy metals, and the parasitic cysts that can cause terrible intestinal distress, and even death. However, chlorine reacts with organic material in the water to form what are called “volatile organic compounds”, or “VOCs”. Carbon filtration units will remove VOC’s; reverse osmosis won’t.

For that reason, good reverse osmosis units add carbon filtration to their systems, which just adds complexity and cost. Reverse osmosis systems will remove nitrates, where carbon filtration systems won’t. In most case, this doesn’t really matter, because the EPA regulates nitrate levels, and your water supplier will normally take care of the nitrates for you.


Reverse osmosis systems remove the calcium, magnesium, and potassium that our bodies need, and that make water taste “alive” and good. Carbon filtration units don’t.

Water Usage

Reverse osmosis units typically waste three to ten gallons of water for every gallon purified.

Carbon units waste no water.

Initial Cost

Carbon filtration systems are typically quite a bit less expensive. Systems from the top manufacturer of home water treatment systems start at about $100.00. Good reverse osmosis units start at about double that.

Operating Costs

Carbon filtration systems cost about $.10 per gallon to operate, while reverse osmosis systems run between $.25 to $.35 because their filters and membranes are more expensive to replace.


Reverse osmosis is slow, so you need a storage tank, which takes up a significant amount of space under your sink. Carbon filtration units don’t require a storage tank.