Having had to carry water to the cabin I lived in for a couple years, eons ago, I'd suggest that you look into bacteria growth and Legionella disease to make sure you don't get any surprises. Storing, draining and refilling over a period of time can create a wonderful atmosphere for bacteria. It is a heck of a way to loose 10-20 lbs
Tank water heaters, the glass lined versions almost always leak at a tank penetration. The specification for their approved construction allows up to 1 sq" of open metal/sqft of glass. In a used tank that had been open to the atmosphere for a period of time the corrosion accelerates. Once the anode is consumed the water looks for something else to "consume" and the open metal is perfectly satisfactory.