Last summer I looked into several ways to cache water in a forest:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=94294
I bought pipe and caps at a local sprinkler supply store, made a cache with a 1.5 liter water bottle, and placed it in the woods in my backyard. Similar to what Nico describes.
Based on this thread, I decided to see how it went after 7 months.

Water cache on the forest floor, between two small logs. Brooks Cascadia size 11.5 for scale.

Dirty, but intact so far. You can barely see white duct tape on each cap.

About 1/2 ounce of water came out when I removed the cap. Probably condensation or rain, about 20 inches fell since placement.
The water bottle was intact. A small taste revealed – tasteless water.
The pipe is some kind of lightweight, ribbed drain or irrigation pipe, approximately 3 7/8 inches inside diameter. Much cheaper than PVC or ABS, but I don’t recall costs right now.
My backyard is in a mixed forest of redwood, douglas fir, oak, and madrone, on the Central California coast. We have seen a wide variety of small wild mammals in our yard, including raccoons, squirrels, rats, mice, voles, deer, bobcats, and mountain lions.
YMMV.
— Rex