Neat little fresh water in an ABS pipe idea

By my calculations a 4" X 60" pipe will hold about 750 cubic inches; converting that to liters results in about 12.3 liters. So, you could, indeed, pour 24 500ml bottles of water into the pipe...

Odd that it's on the driver's side. Not very safe if parked on the roadway?
3.25 US gallons is 12.3L of water. That's a case of 24 X 500ml bottles of water.
I don't think there's any way you'd get a case of 24 X 500ml water bottles into that pipe, if the 4" by 60" dimensions are accurate.

Actually it's a good idea. Simple, cheap and effective.

Long coast, lots of beach to surf, not everywhere is a state park with showers
3 gallons warm fresh water to rinse off salt and sand

I would suppose to take a shower(rinse off}

for what purpose?