Trying different method of fresh water tank sanitization

30+ years of RVing and I never sanitized fresh water tank.
But quite often, when leaving campsite going home, I open the tank drain and driving motion leaves only some water residue for the storage.
On few occasions, when in CA earthquake zone I would keep some water in the tank for emergencies. That never develop bad taste thru the winter, but we had good water supply in Bay Areas.