How it began
The system was built by the ancient Maya at Tikal, in what is now northern Guatemala. Researchers from the University of Cincinnati found a mixture of zeolite and coarse crystalline quartz in undisturbed sediments of the Corriental reservoir, an important source of drinking water for the city. Six radiocarbon dates show the water was filtered through these minerals between about 2,185 and 965 years before present. The authors call it the oldest known example of water purification in the Western Hemisphere and the oldest known use of zeolite to decontaminate drinking water anywhere.
Before it existed
Tikal's reservoirs were built and maintained from the early settlement of the city, about 2,500 years ago, and collected runoff that had to carry a large population through dry seasons. Other reservoirs at the site show contamination from heavy metals, toxin-producing algae and a mineral associated with fecal pollution. Corriental had significantly less, which led the team to look for a filter.
How it works
Zeolite is a volcanic mineral that is still used for filtration today. Sand-sized quartz crystals on their own could clarify water but would not remove harmful microbes or toxins, which is the work the zeolite did. The Maya brought both from a rock formation at the Bajo de Azúcar, about 30 kilometers northeast of Tikal, where an aquifer is known locally for clean water. The filter was probably held behind dry-laid stone walls and woven reed or palm matting at the inlets of the reservoir.
What changed first
The filter gave the people of Tikal safe drinking water for more than 1,000 years. Flash floods periodically washed filter material into the reservoir, leaving layers of quartz crystals that record its repeated use and renewal. Tikal reached its peak population around the seventh century.
What lasted
The study, published in Scientific Reports in 2020, places the system about 600 years before the sand and gravel filtration described in the Sushruta Samhita of South Asia and about 1,800 years before the sand filter attributed to 1627 in Europe. Kenneth Tankersley, a co-author, said the system would still be effective today. The reservoirs were abandoned with the city about 1,100 years ago.
