I'm at the water pump, I cannot find the water filter part that is required to finish the quest, where..

I suppose you're talking about that lamp like water filter. You can find it in Murdock's crate which you can get from murdock at Junkyard. Be ware, there will be so many zombies and trashman zombie with 800hp. Heavy toxic damage. Take some good weapon, lots of berry juice/water/bandages. You can kill trashman multiple times as each time you'll get 30chocolates, which you can trade 20chocolate for each crate. Don't die in there with trashman. Rest you'll know when you're inside.

That's a specific filter that's in the back of the main raider camp across the chasm. It's in a crate