[JCavilia]

Depends on how much water we are talking about.

More than likely, if it is only a small.. tiny amount.. it is the moisture in the air that you pump into your tire condensing when the tire warms up due to friction (even in cold weather).

1. Reading comprehension issue: He said water in the TIRES, not in the tubes. He also said this only happens after a long ride in the rain.

2. Physics issue. Water vapor condenses into liquid when the air containing it COOLS, not when it warms up. Conceivably, if you pumped up the tires on a very warm and humid day, some of the humidity could condense when the bike later sat in the cold.