Confused about the clean water crisis?

I saw this commercial for a charity and it said 1.1 billion people don't have access to clean water. What I don't understand is why simple purification methods aren't used. In survival handbooks, they always tell you how to filter water using rocks or cloth, about boiling it for purification, and about those purification tablets. These methods seem rather cheap and easy to use. Why aren't charities, or even impoverished villages themselves, using these methods to fix the crisis?