Tap water smelt foul in the house, the smell was faint and we kept using the water for a week for drinking, cooking and bathing. When the smell became discernible we got the water tank cleaned and found a dead garden lizard in it.Water tank cleaned with bleaching powder

As yet feel no symptoms of ill health - please advise

The lizard likely drowned, and sometimes water does smell a little off (I used to go to a summer camp where the water had a slight sulfur smell but was very safe to drink).
I wouldn't worry too much... Don't use bleach in your drinking supply though! That is way more dangerous.