Yo. Those who’ve played this game may remember a tunnel in Blackwater City that fills up with water as you run through it. My son can’t get through there without drowning (as Ratchet, you understand). It is upsetting him mightily. So, do you need to [ul]
[li]Run faster[/li][li]Stop the water from rising somehow[/li][li]Get a piece of equipment that will help you; or[/li][li]Go somewhere else entirely?[/li][/ul]
Please help, for the sake of a 7-year-old’s tears! 
Essentially, the answer is run faster. There’s no equipment (other than Clank’s helicopter pack, which you get in that city with the flying train) to help him and no way to stop the water from rising. The way to run faster is to use the run and jump move that comes with the helicopter pack. I can’t remember how do do it without the game in front of me, but when you get the helicopter pack, it tells you how to jump farther by (I think) holding down a button while you’re running and releasing it when you’re ready to jump. If he uses this as much as possible while running through the tunnel, he should make it.
Thanks! I’ll pass it on and we’ll see how he gets on.
That’s definitely one of the more challenging parts of the game. Like Nuveena said, there’s no real trick–you just have to move quickly.