I recently took on some adult piggy girls that were in need of a new home. They are very lovely and have settled in well. I had lots of piggies when I was a child/teenager but this was a few years ago

I'm sure they get everyting they need, I have been reading up about stuff on forums and websites. They get fresh veg everyday, fresh hay daily, cleaned out 3 times a week, and they have been going out in their lovely, big run that OH built them (he got a bit carried away!!). Oh, and they also get pellets (burgess, I think?).
I am a bit bewildered as to why they never seem to drink though? The water bottle does work as they drank a whole bottle overnight on their first day here. I check it works, have changed it for another, but still they don't drink. I even gave them a bowl of water but they weren't interested when I put it in
I am perplexed. They are not young ladies and I worry about their health with not drinking