We are charged extra for water usage above 'normal' use - so I pay for hay soaking as do some others, a few pay extra for the amount of bathing/show prep they do.
I used to factor water costs in and it was included in monthly livery bill.
New liveries were told that water was usually included, but as the yard was metered, then water was to be used when necessary and if I found that usage was excessive then I would be charging them the extra over. Only ever had one that always used lots, the same one that 'forgot' to turn off the hose after use too. She did get invoiced for the cubic metre it cost me extra each of 3 months she was with me.
The reason we have to be careful without going into detail how it happened. We had the water board round many years ago say 15 for argument sake, our pipe must have got damaged and water leaking out, the water board could see there was no evidence on our property but still fined my husband a substantial about of the total bill which was £ 70.000 as was leaking a long time.
No ours is a working farm for cattle and sheep with various large automatic troughs. The horse buckets are the only manual buckets so we are not asked for extra.