It seems that some people are unaware of the scrutiny that happens now in FEI stabling.
The loose stallion that injured the mare was something that the FEI did not want repeated, and now the administration of meds or fluids without the knowledge of the rider or owner (remember Nicholson’s lack of anger management towards the vet and the kerfuffle surrounding that, and now the recent death of Chromatic the jumper) have resulted in changes.
It took a long time to get the rules to address those wrongs, but the requirement of food and water have been on the list for quite awhile. If the stewards miss it a fellow competitor will notice.
When I did night check for the barn (USEF shows), I did as @endlessclimb does. Looked at every horse on both isles. When I was the only one there, it didn’t take that much longer than just tucking up ours (we had at most 8) and lack of water would certainly be noticed.