Excessive drinking and urination

I have a 3.5 yr old male mini lop. About 3 days ago, I ran out of pellets and have been unable to visit the store for more. So he's been sticking mainly to hay and fruits/veggies. Since then, I've noticed that he's been drinking and peeing A LOT. Usually when I change out his water bottle in the mornings, he'd only have drank about half, but he's going through 2 bottles in one day. I just cleaned out his litter box last night and when I looked in it a few minutes ago, it looks like a lake, there's so much urine in there that the litter isn't soaking it up (thank goodness there's a bar cover so he's not standing in it). He's not acting depressed or lethargic, he's acting like his usual self. I'm picking up pellets in the morning so he'll be able to eat his usual diet. Should I be concerned?
Thank you!

Any chance the water bottle is leaking??

Pellets contain lots of vitamin's and nutrients and by running out of your pellets your rabbit may be drinking so muck because he is trying to get the vitamins and nutrients out of his water. Chances are that once you get pellets give him a day or two and your rabbit should be back to normal. Best of luck:bunny22::goodluck

Did your bunny stop drinking and peeing as much after you got the pellets? I noticed my bunny doing the same thing this week when I started limiting her pellets.

We have an overweight bun, and she had her pellets limited, and she started drinking more and more. We were only feeding her once a day, so we started feeding her twice a day (1/2 in the morning and 1/2 at night) and making sure she had plenty of hay, and she stopped drinking as much.