Most water carries micro organism. When that water is stored in a very enclosed space (just like a motorhome new water tank) microorganisms can multiply quickly. This will become even worse in warm temperatures. Legionella is amongst the key considerations, but so is E-coli and several other kinds of microbes. https://lanexg1i1.bloggadores.com/30391612/the-greatest-guide-to-how-to-clean-and-sterilize-water-tanks-in-buraidah