Water is a scarce and valuable resource in the Galapagos and always has been. Only a few of the islands have regular springs where people can find water. The presence of water depends mostly on rainfall, which happens only between January and June, the wet season. The amount of rainfall is different from year to year and from island to island. But the greatest variation is a result of altitude. The highlands receive a lot more rain than the coastal areas and are a better place for most plants, animals, and people to live.
Most of the underground pools and springs are found only on the older islands, like San Cristobal, Santa Cruz, and Santa María. Here, thousands of years of erosion created pockets and caverns deep underground where rain water and dew could pool and be collected. Patrick Watkins figured this out pretty quickly and managed to survive here for years. Others weren't so smart, or so lucky.