toilet tank condesation

What might cause this?? Last night we had about 3 couples and their kids over. At the end of the night, I noticed the tank on the newly installed toilet had a bunch of condesation on it and it was dripping all over.

The only thing I can think of is that it has been really cold the last few weeks, temps in the single digits. Then yesterday we set a record high of high 60's for the day.

The only thing I can figure out is that because of the really cold weather, the water in the ground is colder than normal and then with the house being warmer than usual with unusual warm temp and a houseful of people, probably using the toilet a bunch. I'm thinking on a normal day, the water set in the pipes long enough to warm up a bit, but with all the people the water kept getting refreshed and the coldest water outside was coming in causing the problem.

Is there anything else that might be at play??? The toilet has been installed for about a week and never noticed this and today, the problem isn't there.

Main lines coming in are copper, then I have pex feeding the toilet.

Thanks for any response....

With that many people using the toilet, it kept the tank cold with incoming water.

The same thing will happen if the tank has a leak. The cold water is like a glass with ice cubes in Summer. The outside sweats.

The fill valve may not be sticking.

So my thoughts are correct, I'm supprised this has never happened before. There might be a small leak on a supply line as well, I just haven't had a chance to correct it.

Thanks for the reply.

Like I said a supply line does have a drip, which should be fixed later today, if I get motivated, I don't think anything inside the toilet is leaking, but I'll check that out as well. Like I said it hasn't happened until last night.

Thanks for the replies!!