Water, water, every where,
And all the boards did shrink ;
Water, water, every where,
Nor any drop to drink.

The very deep did rot : O Christ !
That ever this should be !
Yea, slimy things did crawl with legs
Upon the slimy sea.

About, about, in reel and rout
The death-fires danced at night ;
The water, like a witch's oils,
Burnt green, and blue and white.
~Samuel Taylor Coleridge

I suppose you could need to gather water in any place K.A. Some places are more likely though.
If you have a plastic sheet or a tarp gathering the rain is fairly easy.
Getting it into storage is the problem.
So bags, funnels, wide mouth bottles and pots are going to be very desirable items to have.

Maybe it makes sense to wonder what you can pack light and contain a lot of water with.
Plastic baggies are an option, some folks suggest condoms inside socks for strength. You likely have a couple of nalgene bottles.

OK, so in your kit how much water storage volume can you get happening if you had to?

I seem to limit out at about 4 gallons. That counts plastic baggies and water bottles. I am not counting my food bowls and cooking pots.

If I count the garbage bags it is much higher but they dont work well to carry water in at full volume. Lets say another 4 gallons in a plastic garbage bag. Maybe a bit mor if you had it inside a packsack.