Presence of heavy metals, in particular more than permissible limit is harmful in drinking water. If heavy metals are toxic in nature than health hazards may be more serious .Further more, there are various toxic chemical constituents, for example Hg, Pb, Fe,, As,  and many more are very harmful if present in drinking water. Presence of   these may be problematic for living organism too.  As to check the problem, it is better to analyse water by ICP-MS / AAS and delineate the problem.

Hello, it depends on the kind of water: there are in many countries special regulations for waste waters and drinking waters, which may be different with respect to limiting concentration values. Many years ago we had a hard discussion in Germany because, for example, the limiting value for copper was set to 0.5 mg/L (mor difficult to achieve for companies) in waste water but to 2 mg/L in drinking water.

Hi Shahabaldin, 

I am not sure if I understood your question, would you like to know about the maximum range already measured in water samples (which is causing toxicity)? Alternatively, you could be interested in the maximum concentration allowed for different water types (in this case, maximum permitted concentrations are assumed to not cause deleterious effects for certain purpose, i.e. not harmful maximum commonly based on the NOEC-non observed effect concentration).

For the first question, there are several studies reviewing metal concentrations in specific types of water from drinkable fresh to industrial and marine waters. A good start for that would be the classic book Metal Pollution in the Aquatic Environment (Föstner U & Wittmenn GTW 1979). Maximum concentrations vary considerably depending on the metal and type of water (fresh riverine-lake/salt estuarine-marine /waste urban or industrial /drinkable), and the metal itself (and solubility limits), the environmental parameters (redox, pH, alkalinity, organic carbon, etc.), and metal species (total concentration, dissolved (0.45µm filtered), truly dissolved (ionic forms) or free ion.  Therefore, toxic maximum measured concentrations on water systems vary a lot, and you'd need to check on specific metals per type of water. However, as a general rule (excluding rare elements) it is normally possible to find a case where metal concentration measured approaches or is even higher than the solubility limit.

In terms of maximum concentrations allowed on regulations they also vary widely depending on the metal and water category. It is important to notice that these maximum concentration on water quality criteria are meant to prevent any deleterious effects. As mentioned by Henry Bergmann, that is why several times drinking water has higher permissible concentrations than environmental samples (i.e. it's been consistently demonstrated that humans are quite resistant to metals compared to other organisms, especially freshwater invertebrates). Additionally, the way environmental limits are established is depending on the country. For instance the US Environmental Agency derive water criteria based on regressions of toxicity endpoints for each metal, thus depending on the availability of data for toxicity of individual metals. As a result, maximum allowed concentrations are constantly updated depending on water properties, and sometimes they refer to dissolved metal or to the total concentration. For metals such as copper, the limit is actually an equation that depends on the water physico-chemical parameters instead a single value. Which is the same situation for Canadian water quality criteria. Differently, in Brazil water limits are depending on the usage the local community  wants to have the water for.  As you can see, also for maximum allowed for all metals there wouldn't be a single reference to mention. There are several reviews to check for individual metals. However, most of regulations consider the issues discussed by Fairbrother et al (Fairbrother, A., Wenstel, R., Sappington, K.,Wood,W., 2007. Framework for metals risk assessment. Ecotoxicol. Environ. Saf. 68, 145–227). Additionally, the reference limit in most of metal studies is the US EPA limit (link below), which reasonable represents most of limits worldwide.

In summary, there might be no single place to get all the maximum (measured or permissible) concentration for all metals. It would be easier search for individual cases (per metal, per water type, in a given region). Once you've narrowed you search it would be easier to get a response. 

Hope it helps.

All the Best

Abel

https://www.epa.gov/wqc/national-recommended-water-quality-criteria-aquatic-life-criteria-table

It depends on guideline in your country. Different country, then different requirement.

Thank you.

Present question is related to (1) drinking water  (2) living organisms so the discussion of waste water is just waste. Already published literature available for guide   lines.

Different countries have their own water quality standards for individual sectors. For drinking water quality purposes, WHO, EPA and EU guidelines are widely used. You can follow the WHO guidelines for drinking water quality.

http://apps.who.int/iris/bitstream/10665/44584/1/9789241548151_eng.pdf 

Dear Shahabaldin Rezania

The maximum allowable limits of heavy metals in water (i.e. Threshold limits) depend on type of water. For instance, allowable limits in drinking water differ from aquaculture water. Standard regularities (e.g. WHO regulations for heavy metals in water) identify this point. Also you can ask about your country regulations regarding this point. Finally, search for researches setting limits for heavy metals in Rivers, Seas, Lakes, drinking water, ...etc.

Kind regards

Ahmed