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At one time, Tikal supported 60,000+ people with no fresh water source (creeks, streams, etc.) nearby.
How could that many people live there at once without fresh water?
The Maya devised a way to collect rainwater. The center of Tikal was on a slope, so the rainwater flowed downhill. They used their natural resources (limestone, clay, etc. mixed with water and baked to make plaster) to their advantage. They created a cistern with the plaster.