Frequent Questions

How are advised standards for Secondary Standards (specifically TDS) determined?

A SMCL for total dissolved solids (TDS) was established
because high concentrations have adverse taste effects which force consumers to
use other water sources.  Highly mineralized water also deteriorates
distribution and domestic plumbing and appliances.


Mineralization has been shown to have an economic impact on
water distribution systems and household plumbing and appliances. 
According to Lawrence, the life of home hot water heaters deceases one year for
each 200mg/L of TDS in water above a typical 200 mg/L figure.

Mineralization can also cause precipitates to form in
boilers or other heating units, sludge in freezing processes, rings on utensils
and precipitates in foods being cooked.
The 1962 edition of the
Public Health Service Drinking Water Standards included a limit for total
dissolved solids (TDS) of 500 mg/L because of taste effects and because
drinking water containing a high concentration of TDS was likely to contain an
excessive concentration of some specific substance that would be aesthetically
objectionable to the consumer

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