This workmanlike set of maps by Ed Bourelle is what it says on the tin: flooded tunnels. Most of the set is interchangeable tiles, but a few terminate in stone tiles. The stone tiles are the connection to other underground sets. The submerged tiles are well-done and look like they’re several feet underwater. The downside to these sets is that the water is uniformly green. This makes the water look fairly brackish. These are not clear water-filled tunnels – it’s more the nasty stuff associated with sewers. But if you’re looking for flooded tiles for a typical dungeon, this will do nicely.
You can purchase this set at DriveThruRPG.