The details of locating water are beyond the scope of this article. The basics are using a map, knowing how water flows through and collects in certain geographical formations (natural cisterns), and identifying which plants indicate shallow-underground water and contain easily accessed water. Heading downhill to streams, and looking for rich, green vegetation that may indicate a spring, are ways to start. Following bees and tracking animals to cisterns, knowing where to dig in apparent dry stream beds, and possibly waiting for night when vegetation releases water, are slightly more advanced techniques. Water can be collected in a clean container. Clear plastic bags can be used to make vegetation and solar stills. Dehydrated, chemical-free sponges can be used to wipe dew from vegetation, or tied to ankles before one walks through damp vegetation in the morning, soaking up water from wet rocks or sand. A flexible drinking straw can access water in a rock crack, or drink from a water still without opening it. Tarpaulins can also be used to collect rain water or dew.