A spring box is a covered chamber built around a spring’s emergence point with an overflow pipe larger than the supply pipe, the supply pipe set 5-10 cm below the overflow level, a cleanout drain and a tight lid. The overflow must pass the spring’s entire wet-season flow: at 5 cm of head a 25 mm overflow passes about 0.29 L/s and a 50 mm one about 1.17 L/s, so a spring of 0.33 L/s needs the larger pipe.
A spring box captures water where it comes out of the ground, protects it from surface contamination and feeds a pipe. It also acts as a small reservoir that evens out the spring’s changes in flow.
The Box Must Not Back Up The Spring
A spring comes out where the water table meets the ground. If the box holds water at a level above the original emergence point, it can raise the pressure on the water behind it, and the spring may find another way out below or beside the box. The parent page warns not to dig into the aquifer, since you risk redirecting the flow. So build the box to capture the spring where it emerges, and set the overflow so the water level in the box does not rise above the original spring eye. The overflow, not the supply pipe, sets the box’s water level.
What The Parent Page Specifies
- Excavate carefully around the emergence point. Do not dig into the aquifer.
- Build a small box of stone, concrete block or earthbag around the spring, open at the bottom where the water enters.
- Overflow pipe near the top, larger in diameter than the supply pipe.
- Supply pipe 5-10 cm below the overflow level.
- Cleanout drain at the bottom with a plugged valve.
- A tight-fitting lid.
- Backfill with gravel for drainage, then earth.
Source Protection adds an uphill drainage ditch at least 2 m from the box (30-50 cm deep, in a semicircle) so surface water goes around it, and a cover that keeps out animals, leaves and runoff.
Worked Example: Is The Overflow Big Enough?
Measure the spring yield with a bucket: 20 L in 60 s is 0.33 L/s, or 28,800 L a day. The wet-season yield may be higher; measure then too, or plan above the dry-season figure.
The overflow runs as a short pipe discharging through a small head. Take the head above the pipe centre as 5 cm and an orifice-style coefficient C_d = 0.6 (a textbook value, recalled). Flow = C_d × A × √(2 × g × h), with √(2 × 9.81 × 0.05) = 0.99 m/s.
| Overflow bore | Area | Flow at 5 cm of head |
|---|---|---|
| 25 mm | 4.91 × 10⁻⁴ m² | 0.29 L/s |
| 50 mm | 1.96 × 10⁻³ m² | 1.17 L/s |
| 75 mm | 4.42 × 10⁻³ m² | 2.63 L/s |
A 25 mm overflow passes 0.29 L/s, less than the 0.33 L/s the spring gives, so the box would fill, back up and raise the water level behind the spring. A 50 mm one passes 1.17 L/s, 3.5 times the spring’s flow. Choose the overflow to pass at least the highest flow you have seen, with margin, and larger than the supply pipe (parent page). Size the supply pipe separately from the flow and head using Pipe Sizing.
What You Need
- Stone, concrete block or earthbag for the box, and clay or lime mortar to seal joints
- An overflow pipe, a supply pipe with a screen over its intake, and a drain with a valve
- A lid that closes tight, with an animal-proof catch
- Gravel for backfill and for the base
- A bucket and watch for the flow test
Method: Capture, Protect, Pipe
Step 1: Expose the spring eye, digging only enough to see where water emerges.
Step 2: Build the box around it with the back wall packed with clay on the uphill side and gaps at the base for water to enter.
Step 3: Set the overflow at the planned level and the supply pipe 5-10 cm below it, screen on the intake.
Step 4: Fit the drain, lid and ditch; backfill with gravel then soil.
Step 5: Direct the overflow and drain away to a stream, ditch or soakaway, well below the box, with a screen over the end against animals.
Step 6: Check monthly for debris, animal intrusion and contamination (parent page), and after every heavy rain.
Common Mistakes
- An overflow smaller than the spring’s flow. The box fills and the spring finds another outlet.
- No uphill ditch. Runoff washes in dirt and organisms.
- A loose lid. Animals and insects get in.
- Digging deep into the hillside to enlarge the box.
- Letting the overflow soak back beside the box.
Safety
Spring water is not safe to drink untreated, and a deep or covered box is a hazard
A spring box can be contaminated by animals, runoff or a latrine uphill; keep latrines, livestock and compost well away uphill (Source Protection) and treat the water (Water Purification). Do not climb into a deep or lidded box: it can be short of oxygen and the commonest fatality pattern is a second person climbing in after the first collapses. Do not test the air with a flame.
What’s Next
- Learn next: Pipe Materials & Construction — choose the pipe the box feeds
- Combine with: Spring Capture — sizing the spring’s yield to the community