How to unlock: Talk to Zeke at Atom Cats Garage (M9,12)
As soon as you walk into Atom Cats Garage, you will be accosted by the leader - Zeke. He suggests that you talk to Rowdy, who gives you this quest. The objective is to get to the Warwick Homestead, nearby Eastwards.
There, you find a water pump, behind the door. Interact with the pump to repair it. Report this to Mrs Warwick, who gives you five Mirelurk Cakes. Then, return to Rowdy.
As soon as you return to the Cats, you will be attacked by gunners. All you need to do here is survive - gang will do well dealing with the enemies on their own. However, if you want to take part in the fights, turn your interest to the enemy robot that can wreak havoc here.
Rewards for completing the quest: Experience points, Zeke's leather jacket and pants, a discount while trading with Cats, five mirelurk cakes.