Basic home water treatment

Scandinavia and UV
Question: 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

Answer: It would be helpful to know what it is you’re 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 or point of entry  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/cm2), unless local regulations specify otherwise (Norway requires 16 mJ/cm2 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.

Filtration, etc., in Israel

Question: We are looking for a water filter for normal drinking water. It’s to be used in our new home which is in Cochav Ya’akov, about five minutes north of Jerusalem. We were told by the water authority’s secretary that there is a big problem of scaling and taste but the water is OK (She would not let me speak to a water engineer!!!). We have looked at several filter systems. Some have one stage; others have three or four (for me, a stage is the number of filters the water goes through, not any internal workings). Is there a need for several stages? Does the number of stages reflect the quality of the product? One of the nicest filter systems we saw is from a large firm but is not a standard size. How important is the standard sized filter in this case? Are ceramic filters different than carbon filters?

Shalom Deitch
Jerusalem, Israel

Answer: A “filter” removes suspended solids. Suspended solids can cause problems with drinking water supplies, primarily due to color and aesthetic appearance, sometimes due to bacteria, infrequently due to bad taste. If the water tastes bad or has an odor, it’s most likely due to organics, although a number of dissolved contaminants and gasses such as hydrogen sulfide (H2S) cause taste and odor problems. Color can be caused by organics, as well as various forms of suspended solids and by certain dissolved contaminants.

Hardness ions such as calcium cause scale. Other ions such as iron and manganese cause staining. Many of the ionized contaminants are removed by water softening. Many of the poisonous contaminants (like arsenic or nitrate or selenium or heavy metals) do not have any taste, at least at the concentrations normally encountered.

Filter housings can be used to contain many medias such as activated carbon, or ion exchange resins that can be used to remove impurities other than suspended solids.
Without more information, it’s impossible to know what’s meant by a “4 stage” filter, but as a guess this probably refers to a series of filter housings that probably contain various media used to remove various contaminants. The number of “stages” should be defined by the types of contaminants that need to be removed. Most drinking water supplies are pretty good quality, and it’s a waste of money to treat for contaminants that aren’t actually present.

Start by defining your problem(s). If at all possible, get a copy of the water analysis and compare it to one of the standards for drinking water contaminants (World Health Organization, American Water Works Association, U.S. Environmental Protection Agency, etc). Find out what’s in the water that’s objectionable (make a list). Next, look at the various medias that can remove those contaminants. Lastly, choose the number and size of housings to contain those medias and give you the flow rate required.

The only concern about non-standard housing sizes is that you may be limited to the medias offered by a single manufacturer and to whatever price they wish to charge you.
If this sounds like a lot of work, it is. If you don’t care to do it yourself you can go to a company that makes drinking water purifiers and seek their advice. Make certain you’re working with someone who is actively doing this type of work for a living, and who is reputable and familiar with the types of contaminants and problems with the water supply you have.


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