Acceptable Levels of strontium and silica in drinking water - Need applicable regulations and other comments

I wish to consult the forum regarding the presence & acceptable levels of Strontium and Silica. The norms/standards for drinking water contained in IS 10500 (Bureau of Indian Standards)  do not prescribe any permissible or derired limit for these two elements.  Some pockets in Andhra Pradesh and Punjab reported presence of silica upto 150 ppm and strontium upto 3500 ppb. Can any of the esteemed experts, participating in the discussion here on the portal, comment on this please?

Information regarding the acceptable levels, applicable regulation & any related comments would be helpful.

Dr D R Prasada Raju
drpraju@nic.in