Scandinavia and UV
I want to ask you how to purify and filter ordinary tap water in the kitchen with the best overall result. Also how do you purify shower water? Please, give me your best knowledge in this home water purification jungle.

Johan Nordenberg

A: It would be helpful to know what it is you are trying to remove from your water. By ordinary house tap water, do you mean a treated community supply or untreated groundwater or spring water. If this is a community supply, is it chlorinated?

Assuming it is microorganisms you wish to remove, and your water supply is chlorinated (and chlorine residual is still present when you run your water), bacteria and viruses are likely to have been significantly disinfected. Filtration would be necessary only for protozoa (Giardia and Cryptosporidium). If there's no chlorine at your tap and you apply filtration, bacteria may benefit from the environment created in a filter. Therefore, in such a case, I would suggest use of point-of-use (POU) or point-of-entry (POE) ultraviolet light (UV) downstream of the filter as an additional barrier. The system employed should be sized to provide roughly 16-to-40 milliJoules per square centimeter (mJ/cm^2), unless local regulations specify otherwise (Norway requires 16 mJ/cm^2 for drinking water applications; Austria requires 40). UV would also offer additional protection against protozoa.

Unless your water is excessively contaminated, it would be cost effective to apply your home treatment system only to the waters being consumed, and not waste treatment on shower water. In other words, use small POU units rather than larger POE systems.

Again, knowing more specifically what you wish to remove from the water would facilitate evaluation of filtration options.