Reverse osmosis, water distillation and carbon filtration compared

There are numerous methods for removing contaminants from water. Each method has strengths and limitations. So, it is best to know…

a.  what needs to be removed from the water coming out of your tap
b.  which method(s) will get that job done
c.  how frequently your filters will need to be replaced or maintenance performed so that your system delivers sustained contaminant reduction.

Water purifiers remove all particulate and specified microbiological contaminants from water – pathogens like bacteria, some viruses, and cysts. Reverse osmosis systems and water distillers are water purification systems.

Reverse osmosis systems require water pressure or a pump to push water through an extremely fine semi-permeable membrane into a holding tank from which the finished drinking water is dispensed. All particulate and, typically, more than half of the original water are disposed of and go to waste. All minerals are removed. The result is very pure water with a neutral or slightly acidic pH. Any desired remineralization and pH adjustment must be applied to the water after it has gone through the RO process.

Water distillers steam water in one chamber and then condense it into a separate collection chamber from which the purified water is dispensed. All particulate and any chemicals that volatilize at a temperature higher than that required to turn water into steam get left behind in the bottom of the first chamber. Only pure water gets into the collection chamber. Water distillers require electricity and time… approximately 5 – 6 hours to produce one gallon of purified water. All minerals are removed.
The resulting purified water has a neutral or slightly acidic pH. As with reverse osmosis, any desired remineralization and pH adjustment must be applied to the finished water after the distillation process is complete.

Water filters reduce chemical contaminants – such as chlorine and VOCs – and particulate that is larger than the spaces in the media that makes up the filter’s matrix. The filtration media is usually activated carbon because it is extremely good at adsorbing an enormous amount of organic chemicals, plus bad tastes, and odours. Activated carbon filters can remove select heavy metals without stripping healthy minerals from the water. The pH of the original water will not be greatly affected, unless intentionally increased with the addition of alkaline minerals.

Carbon filters are made from granular activated carbon (GAC) or powdered activated carbon (PAC) derived from coal or charred coconut shells. One gram of activated carbon has an adsorbent surface area exceeding 3,000 m² (32,000 sq ft). The surface area covered by one teaspoon of activated carbon is approximately the area of a football field.

Reverse osmosis systems and water distillers usually incorporate carbon filters to adsorb the chemicals that the RO and distillation processes do not intercept.

Granular activated carbon (GAC) particles are relatively large. In a water filter these loose granules are contained so that they adsorb a wide range of contaminants as water is passed through them.

Powered activated carbon (PAC) can be fused into a carbon block with a binding agent.

Ceramic purifiers have a thick shell formed from a mix of diatomaceous earth and other select minerals that are fired at very high temperatures. If the pore size of the shell is made fine enough to intercept microorganisms, and the interior of the shell is filled with high quality GAC, the result is a cleanable purifier and filter combined. No binding agent is required.

Note   Manufacturers of water filters and purifiers state limitations on the contaminant load that their device can safely protect you from. Don’t expect to put septic water through a drinking water treatment device even if it is rated as a water purifier. With challenging water conditions, it is wise to apply more than one barrier of protection (appropriate for use with the characteristics of your water source) to achieve a desirable and safe quality of water.