Cisterns

In places, the water run-off from the sewers collects in great cisterns underground. These tanks tend to hold 1d10+10 feet of water, with 1d6+4 feet of air space between the water and the ceiling of the cistern.

The pipes leading into the cisterns enter high in the wall, so any water carried by a sewer pipe spills down into the cistern.

The pipes flowing out of the cisterns are sealed off with iron grates. The grates are locked (the locks are out of the water), but can be opened if the lock is picked. The bars are not too difficult to bend, either.