I assume you're actually asking what we think about making these numbers the legal limit for drinking water?

Those actually look a lot like the concentrations in the water we drink here in Texas, but we have no set limits on these. I would like to see stricter limits put on Ca and Na because they make the water taste very bad, but there is no good way to remove Na or Ca from the water other than RO/Distillation which is very expensive and we like our water to be cheap because we need a lot of it. I can't think of any areas off the top of my head where K has been a real problem, so I think maybe 0 is too low. It's not like mercury or arsenic. I can see a valid argument for setting a limit on Mg though.

Thanks Dr David, yes that is what I really mean.

Those values are used for most of the drinking water in KSA .

I'm not exactly sure what your question is, and I don't know what the MPL abbreviation stands for. These all seem like fairly low major ion concentrations (obviously K=0 is low). Much literature indicates that Ca and Mg is a good thing, and that waters with moderate hardness are beneficial. Too much hardness or dissolved solids poses problems for plumbing; too little hardness poses other kinds of problems. See: http://www.sciencedirect.com/science/article/pii/S0278691502000819# and http://whqlibdoc.who.int/publications/2009/9789241563550_eng.pdf . Having K = 0 mg/L in drinking water is probably not a bad thing, as long as people are getting sufficient K in their diets.

In this question , only cations have been mentioned ,what about anions. In hydro-chemistry, ions are ingeneral present in pair form.Therefore every water analysis data report should show cations and anions. Presently after using only 4 cations, it is not proper to justify for any conclusion.