What would make the water coming out of the faucet from a cistern smell like gasoline or related chemicals?

I just stayed at an AirBnB on a property just outside Ensenada in Baja Mexico.

The water coming out of the faucets smelled strongly of gasoline or some other liquid petrochemical...however I did not see any sort of oily film on the water.

When I reported this to the off site owner he insisted the cistern was just recently installed and the water was safe to drink, and that the guy who just recently installed it told him he needed to put some sort of treatment in it and it would make the smell go away.

I didn't want to chance it and got a refund. But I am curious.

As far as I know the ONLY thing that is going to make water from a cistern smell like this is contamination from liquid petrochemicals - am I right?