A spring box is a watertight enclosure built round a spring eye that collects its water and passes it into a pipe: dig out the eye gently, build a permeable back wall of dry-stacked stone or gravel, build watertight side and front walls with an outlet, overflow and drain, pour a sloping floor, cast a lid with a lockable hatch, and backfill with gravel and clay. The standard size is 1 m wide, 1 m deep and 0.8 m tall, and it should be built at the end of the dry season, once the flow has been measured through a full year.
Part of Spring Capture
A spring box is the standard structure for capturing a concentrated spring. It protects the eye from contamination, gathers the flow into one outlet and gives a place to inspect and clean.
The Box Has Six Jobs And Each Part Does One
The Spring Capture guide’s design divides the work among six parts:
| Part | Job | Detail |
|---|---|---|
| Back wall | Lets spring water in | Permeable: dry-stacked stone or gravel, never cemented shut (Inlet Wall) |
| Side and front walls | Hold the water and keep surface water out | Watertight: mortared stone or poured concrete |
| Outlet pipe | Takes water to the supply | 32-50 mm, set 10-15 cm above the floor (Outlet & Overflow) |
| Overflow pipe | Takes surplus away | Same size as the outlet or larger, 5 cm below the top of the walls, with the walls cut so that this puts it at the level of the spring eye (Box Design) |
| Drain pipe | Lets the box be emptied and cleaned | At the very bottom |
| Floor and lid | Seal the base and the top | 8-10 cm of concrete on a gravel base, sloping to the drain; a reinforced slab with a lockable hatch, overhanging the walls by 5 cm |
Build In The Dry Season, After A Year Of Measurement
The weakest flow is the one to design for, and it is also the easiest time to work, with the eye visible and the ground at its driest (Seasonal Monitoring). Do not build until you have a year of readings, because a box built on a wet-season guess is the commonest error in this work.
What You Need
- Dry-stack stone or clean gravel — for the permeable back wall and gravel behind it (20-40 mm, at least 30 cm thick)
- Mortared stone or concrete — for the side walls, front wall, floor and lid (Concrete Making)
- Pipe and fittings — outlet 32-50 mm, overflow, drain, screens (Casing Materials covers pipe choice)
- Reinforcement for the lid — bars or mesh
- Clean water and bleach or other disinfectant for the finished chamber
- A diversion ditch dug first (Uphill Diversion)
Method: Six Steps
Step 1: Excavate carefully. Expose the spring eye by digging about 1 m behind it and about 0.5 m below it, working gently (Excavation).
Step 2: Build the back wall. Dry-stack stone or place gravel on the spring side so water flows through it freely (Inlet Wall).
Step 3: Build the side and front walls. Use mortared stone or poured concrete, to a box 1 m wide, 1 m deep and 0.8 m tall, adjusted to the spring (Box Design). Set in the outlet, overflow and drain pipes as the front wall rises.
Step 4: Pour the floor. 8-10 cm of concrete on a gravel base, sloping towards the drain.
Step 5: Cast the lid. A reinforced slab with a lockable hatch, overhanging the walls by 5 cm all round to shed rain.
Step 6: Backfill. Place clean gravel (20-40 mm) behind the permeable wall, at least 30 cm thick, then backfill the box with clay or compacted earth, mounded to shed water (Backfill & Protection).
Then: let the concrete cure damp, test the box for leaks before covering it, flush and disinfect it, and test the water before anyone drinks it (Community Water Testing).
Worked Example: Volume And Floor Concrete
Inside, the box is 1.0 × 1.0 m in plan. At the overflow level, 5 cm below the 0.8 m top, the water depth is 0.75 m: 1.0 × 1.0 × 0.75 = 0.75 m³ = 750 L. The floor, 8-10 cm thick over the 1.0 m² footprint, takes 0.08 to 0.10 m³ of concrete. With a spring flowing 10 L/min the box fills from empty in 750 ÷ 10 = 75 minutes.
Common Mistakes
- Cementing the back wall. It blocks the spring and the water finds another way out.
- Building without a year of measurement. The box may serve a flow that is not there in September.
- Building before the diversion ditch. Runoff floods the work and fouls the spring.
- Skipping the leak test. A leaking box lets the surface in.
Safety
Cut banks, wet concrete, and confined chambers
A deep cut into a hillside above a spring is a collapse hazard: slope or shore any excavation deeper than 1.2 m, keep spoil at least 0.6 m back, and never work alone (Excavation). Wet cement burns skin and eyes. A closed box is a small confined space: do not put your head or body into a closed chamber to clean it; open the hatch, let it air, and clean from outside with long tools where possible.
What’s Next
- Learn next: Excavation — exposing the eye safely
- Combine with: Piping from Spring — carrying the water to the community