Gravity.
https://www.emergency-wash.org/water/en/technologies/technology/gravity
👉🏼 PDF: https://app.box.com/s/nzuicymnvmkwbtu06r5gfjyjft16rfwa ___ Gravity can be used as an energy source for transporting water by taking advantage of differences in elevation to move water (usually via pipelines). This can occur either from elevated water sources to storage tanks and treatment facilities or directly from elevated storage facilities to supply points. It can be used in many different stages in a water system and in all phases of an emergency.