Water is a rather important resource for our species. Without it, we cannot survive, and so the Lord aptly describes Himself as "the fountain of living water". But of course, water, on its own, is not always helpful, and more often than not, it can actually be dangerous.
Although the world is around 70% water, how much of it would you actually be willing to drink? It is a sad fact that not everyone on earth is as privileged as we are. We are so rich and technologically developed that we can not only add flavours to it, but we can afford to flat out refuse to drink it. I personally don't often drink water (though ironically, this may have been a detriment to my health, which further proves today's point).
But while we in the West have the privilege of being able to say no to water if it's not cold enough, if it's not a specific brand, if we don't like the taste of water in general etc. many people around the world work ridiculously hard to acquire polluted water. Water that we know is not safe to drink, they have to drink. The result? I probably shouldn't need to explain. Let's just say it's not healthy.
But praise be to God, there are plenty of charities around the world dedicated to providing clean water to even the poorest of villages. But there is a problem. Well, there are numerous problems. It's obviously not easy to supply clean drinking water to 7 billion people around the world. This is especially true for non-profit organisations trying to help people living in dry climates. However, one of the major problems is education. This is yet another benefit we take for granted in the West, but is woefully inadequate elsewhere. In the West, we learn about things like germ theory at a very young age. We all know the importance of personal hygiene, and if you want to work with food or drinks, you need extra knowledge on how to do that, and no one bats an eye. But some charities struggle with educating the people they're trying to help on why clean water is important. They often don't understand why the water they've been drinking for their entire lives might be a problem, and when you try to explain what a germ is, they start to think you're crazy.
This is why God calls Himself the fountain of living water. He is essential, and He is sufficient. No other religion can save the soul, and adding things to Him is often toxic. Let us never repeat the mistakes the people of Israel made. God, and God alone, gives us life. Man made cisterns are pure poison.