if i pour water & feed without cleaning & washing the bowls, clean fresh water remains there, i tested it.
It has been a clear cut instruction passed over generation(s) wash clean & dry the bowls before pouring fresh water and feed. do it before doing wazoo and offering fajr
in 2014 after an incident of attempted forced entry i moved both bowls inside the gate as close to gate away from car paths as possible for a week it stopped to disappear then it resumed and continue to date