You can bring more water than just the 5 water pouches. You just need to not drink it all earlier so you have some left when you leave.
There are two actions which gives you different water items. "Extract Water" gives you small water bottles but has a limited number of uses, while "Take Water Pouch" gives you a water pouch and has unlimited uses. So as long as you don't drink all the water bottles early on, you can take 5 water bottles and 5 water pouches on your journey. And that is enough water to reach where you need.