But once it's fixed, all three of the leaks will be rectified (considering you went in the order we suggested). It's the only way to jump to this location, thus making it the hardest leak to fix. The leak is located near that statue, but to get there, you're going to have to climb to the buildings and catwalks far above the statue, so you can access it from above. To the right of it, you'll see a statue of an atom, complete with subatomic particles swirling around it (also in statue form). Head to the nuclear bomb at the center of the town and look up towards the Children of the Atom's building. The third leak is the hardest to find, but once you know where to look, it's a breeze to find. That particular leak will be on your right (there shouldn't be a pipe on your left whatsoever there). The second one is at the back end of the settlement on a virtually identical steep pathway that you will have to climb up. The first is perhaps the easiest to find head to the entrance into Megaton and run down the steep pathway to the lowest level of the settlement. All three leaks are rather obvious if you know where to look. All you have to know is the locations of the three leaks. Now, this side quest can be undertaken in literally two minutes, from front to back. He'll tell you, amongst other things, that the water pressure is down in town because of three leaks strewn around the city. When you arrive, speak to the cranky Walter. Walter is the proprietor of Megaton's water treatment facility, located east of the entrance to the settlement (run up the steep steps and follow the linear pathway from there it'll be the first building on your right). The second is that you have to do this while Megaton still exists (so if you plan on blowing the place sky high for Burke with the city's undetonated nuclear bomb, do this first). There are only two requirements - one is that you have to have a repair level of at least 30. The first time you arrive in Megaton, early on in the game, you'll be able to undertake this side quest, and as long as you don't kill the character responsible for the side quest (a man named Walter), you can do it at anytime. This is an unnamed and extremely brief side quest offered up by the game.

Fallout 3 megaton water leaks