Wow, the ER should have given him more info. I'd strongly suggest getting him in to see a urologist as soon as you can.
Drinking lots of fluids will help it pass a bit faster, but every time it moves, it will hurt. Don't be entirely surprised if the pain killers don't seem to do much. They have always given me vicodin or extra strength vicodin, but it never did much. The only pain killers that really worked were those they gave me by IV. If what they gave him doesn't work, talk to his doctor and get something stronger. I've found that when I am passing them, it hurts like heck, but one of the worst parts is the lack of sleep. Being tired and in pain can make him a mighty bit cranky, so be ready.
Did they give him a "catch basket"? If they didn't, talk to the urologist and see if you can get one. If he can catch the stone, they can analyze it and tell him what kind it is. With that information you can adjust diet and that can help lessen or eliminate them.
I used to crank one out every year about this time. The heat makes it harder to get enough water. I have trouble getting enough water to stay in my gut to keep my kidneys flushed. My doctor gave me a mild diuretic to help. Seems to be working so far.
Tell him that kidney stone pain is one of the worst pains I have ever felt. It hurts more than when my stricture closes up, and it hurt way worse than when I broke my hip. He has my sympathy.
Remicade, 6MP and a few of their friends.
"I'm just along for the ride."