That frog story is NASTY. Yuk.
I always run the the hose free a bit before filling the tank, flushes bugs, stink, amphibians, stale water, etc out of hose.
I filled my tank (only once) from the marina next to mine. A week later my water stunk. Talked to the locals there and they said the well water sucked and so did whatever treatment system they use. I had to manually clean out my tank. Now I fill with known good water and no problem since.