The PCT in Southern California does not have easy access to reliable water sources. The various maps and other resources have special annotations telling hikers where to find water on or near the trail. Sometimes it can be from 15 to 30 miles between reliable water sources. As a result the hiking community has at times “hidden” water on the trail for the hikers. These secluded spots typically have gallon jugs of water and are called “water caches”. The unwritten rule is to fill up only what you need to get you to the next reliable source. Naturally hikers should not rely on these sources because previous hikers could have used them up. However the trail angels who provide these caches are very good at keeping them stocked. Here is a pictures of the water cache at the Anderson’s Oasis around mile 471.