Need suggestions to get rid of worms in overhead tank in Bangalore, Karnataka

I'm staying at bangalore, we have 2 sumps, one with borewell water supplied by local panchayat and the other with corporation drinking water. we pump both the waters to overhead sintex tank for our household use. quiet often we find worms getting accumulating in the overhead tank which in turn is supplied all over. kindly suggest us how to get rid of this, is it dangerous as we use that water for gargling and washing utensils.

Absolom L. Glonite