Best personal tip I've got from experience is to always check the quality of the water before you fill your tank - even in the US. We pulled into a marina somewhere on Florida's ICW
right at sunset, and wanted to get an early start the next morning, so I just grabbed the hose and filled up the water tank from the hose bib on the dock pedestal
before we walked to a restaurant for dinner. On the way back to the boat, I see the sign on the dock
- 'Non-potable Water'.
Man, was it nasty! Really sufurous and oily smelling. Had to pump it all out while underway the next day. Then add a couple of cups of Clorox, refill and pump out twice more to get rid of the smell. A few weeks later, the pump filter started getting clogged with that clear, slimy algae that grows in water tanks
, so had start all over and really clean it this time.
Ended up burning out the water pump before we finally got all that nasty stuff out of there.