APPENDIX VII/WATER FILTERS: REVERSE OSMOSIS
This form of filtration is only available in plumbed-in units. It uses a membrane with microscopic holes in it that only water molecules can get through. Tap water is held in one chamber and water molecules slowly seep out into the other. It removes the vast majority of organic pollutants (but see below), and takes out fluoride, lead, aluminium and other metals, unlike the activated carbon filters.
Unfortunately the process is very slow (even the best filters only produce 5 gallons a day) and uses up large amounts of tap water to produce a relatively small amount of filtered water (up to 10 gallons per filtered gallon). Many of the natural minerals in the water are removed at the same time, leaving a product with an indifferent taste. Without minerals, water loses its characteristic flavour, and since we probably need certain amounts of minerals in our water, this highly purified water may not even be very healthy.
More worryingly, a few molecules can get through the membrane along with the water, including some chlorinated compounds which are known to be injurious. These tend to concentrate in the filtered water, making the original problem worse. This difficulty is easily overcome, however, by combining the reverse osmosis unit with an activated carbon filter. Systems of this type produce a water of very high purity, which may be needed by some patients with severe chemical sensitivities. However, the problem of low mineral content has still to be overcome, and anyone drinking this sort of water constantly may need a mineral supplement. Expense and slow filtering speed are the other main drawbacks to this type of system.
Some doctors report that patients with extreme sensitivity to chemicals react to water that has been in contact with plastic, because minute quantities of material leach out of the plastic into the water. This is unlikely to be true except for a tiny minority of highly sensitive patients. Where such problems are suspected, reverse osmosis units in non-leaching plastic or stainless steel housing are a possible solution. The former are available in Britain, but stainless steel units are only sold in the USA, and the cost of importing one is likely to be very high. Check that plastics really are the source of the problem before pursuing this option. Drinking mineral water in glass bottles for a while should provide a good test. If you are s’till having problems on this type of water, write to the manufacturer to check that the water is not stored in plastic before bottling. Always bear in mind that it could be something other than water causing your symptoms.
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