Toilet

Drinking from a toilet in Fallout 3 can regenerate health but increases radiation at the same time. Toilets are generally a bad choice when trying to restore health, as the Rads:Health Points Ratio is quite poor.

The toilet in Tenpenny's room in Tenpenny Tower has 0 rads, one of the few (other than those in the Tranquility Lane simulation in Vault 112 or in Vault 101) giving 0 rads when drinking toilet water in the game.

Booby trapped toilets
Some toilets may be booby trapped, and have wires linking to 35 microfusion cells, which will give you a mild electric shock. If you attempt to drink from these, your screen gets a small shake, and you lose health. To disarm the trap, target the microfusion cells and press the activate button. If your repair skill is high enough, you can disarm it and retrieve the microfusion cells.