This comes from Samuel Taylor Coleridge's work The Rime of the Ancient Mariner, and it is used to signify that despite being surrounded by something, you cannot gain from it. Coleridge based this on actual events in his life. The first part of the question refers to water everywhere except where the mariner sails. This is because there are two islands in the South Pacific where ships often get wrecked: one is called Vanuatu and the other is New Zealand. There is no water on these islands except for small ponds filled with rainwater or melted snow. It is estimated that more than 4,000 people die every year due only to drinking impure water. This happens especially in countries where poverty is high and where there is no system in place to prevent people from wasting their money on fake doctors who charge them a lot of money for a simple treatment. In Africa, many people do not have access to clean water, so they use what little water there is by planting crops that need a lot of water such as corn and sugar cane. The problem with this approach is that it can cause farmers to move away from growing food and start producing more sugar crops which require a lot of water. This idea comes from the theory of economic growth proposed by economist Karl Marx.