GUATEMALA: Some 2,000 years ago, the Maya inhabitants of Tikal struggled to consistently access clean drinking water. To solve this problem, they created an ingenious water purification system using the minerals quartz and zeolite. It is the oldest of its kind in the Western Hemisphere. The minerals were obtained from a source 18 miles away and brought to the Corriental Reservoir outside the city, where they were used to filter out harmful microbes, heavy metals, and other toxins.