SINGAPORE --- “Just turn on the faucet.”

That’s the answer most Americans and others in the developed world would give if asked how to get plenty of clean water. But for about two billion people, such a response is meaningless. These people – almost a third of the world’s population – do not have access to water that can be drunk without adverse health effects. An even greater number lack access to adequate sanitation, which is a principal reason that more than two million children die of diarrheal diseases each year.