Gravity-Fed Water Systems

Gravity-fed piped systems deliver water from a high-elevation source to a lower distribution point with no pumping energy required. Properly designed, they are nearly maintenance-free and can serve communities for decades.

Key Concepts

• —Head pressure: every 10 meters of vertical elevation difference between source and outlet produces approximately 1 bar (100 kPa) of pressure; this drives flow through pipes without any mechanical assistance.
• —Pipe sizing and friction loss: flow rate decreases as pipe length increases and as diameter decreases; for long runs, larger-diameter pipe maintains adequate flow even with modest head.
• —Intake protection: the spring box or intake structure captures water at the source while excluding sediment, leaves, and animals; a fine screen and a covered concrete chamber are the minimum standard.
• —Break-pressure tanks: on steep slopes, pressure can exceed pipe strength; a small open tank mid-route resets pressure to zero and allows the system to resume at lower head.
• —Distribution points: a single community tap-stand with a drainage apron is easier to maintain and monitor than household connections; it also creates a social space that reinforces hygiene norms.

Practical Guide

1. 1.Survey the elevation difference between source and intended outlet using a water level (a clear hose filled with water acts as a U-tube level over long distances); you need at least 5 meters of head for useful flow.
2. 2.Protect the spring by building a spring box: a covered concrete chamber around the emergence point, backfilled with gravel to filter sediment, with an overflow pipe and a screened inlet.
3. 3.Size the distribution pipe using the rule that 25 mm (1 inch) polyethylene pipe can carry 10-15 liters per minute with 10 meters of head over 100 meters of run; use larger pipe for longer or higher-demand systems.
4. 4.Lay pipes in shallow trenches (20-30 cm deep) to protect from UV degradation, freezing, and physical damage; avoid sharp bends and use manufactured fittings at all direction changes.
5. 5.Install a sedimentation tank (a simple concrete box with baffles) between the intake and the main pipeline to remove suspended particles before they enter and clog distribution lines.
6. 6.Build the tap-stand platform from concrete with a drainage channel leading water away from the standing area; this prevents muddy conditions that encourage bare-foot contact with wastewater.
7. 7.Flush the system completely before first use by opening end caps and allowing water to run until clear; inspect and flush seasonally after storm events that may introduce sediment.