I'm getting ready for a tour of Big Bend Park in S. Texas. Water is a definite concern.

I have 4 btl cages on the bent, but feel I need 2-4 liters more. Will be no room left in panniers for extra bottles.

I'm looking for a bladder that will fit/hang behind the webbed seat of my bent, in a space 2" deep and about 14" wide. And I don't want to pay more than about $10-15 for it, as it'll be a one time use.

Anybody got any ideas/experience for/with an inexpensive, reliable bladder? A DIY?

The first thing that popped into my head was this https://cascadedesigns.com/en/platypu...ulator/product

It's more expensive than you wanted, but the case has D-rings which would allow you to easily hang it even from the outside of a pannier. That said, the Platypus bladders by themselves are extremely reliable. I have two 3 liter ones that have been going strong for over 3 years and I'm a bit rough on such things, so that says something. You could maybe rig your own bag to sling it behind the seat.

Thanks. After posting the question, a buddy volunteered that he had three 2 liter Platypus bags he'd loan me.

Camelbak Unbottle 100 is my choice here in the high desert...mounts right next to my seat.

Check Wal-Mart - they sell some fairly inexpensive bladders.