Food for thought… If the galvanized coating on the INSIDE of the tank is less than perfect, it may not actually be safe for storing drinking water. Zinc is the main component of galvanizing, and it's generally safe. Even good for you, in trace amounts. But older galvanized coatings also contained small amounts of lead and cadmium, which AREN'T safe if they leach into your drinking water.
Engineering: Finding complex solutions to simple problems you didn't even know you had.