Sister's dogs problem?

My sister has 3 dogs. 2 are out back in a pen. One is in a cage and is rarely let out. Only for toilet. The other day I was babysitting the kids. Looked outside and decided to give the dogs some water. There bowl is a huge old saucepan. I filled it up. But before I even had the chance to fill it all up. The larger dog drank it like he hasnt had a drink in days. The smaller dog had a little. I gave all dogs water. They dont even let them out for walks. Also their pen roof is clear plastic. Its been very hot lately. I have dogs and don't do that. I have one outside who has water all day. Really don't know what to do