A drainage pad is the concrete apron under a communal tap, 1.5 meters square and 10 centimeters thick, sloped 2% away from the tap to a channel that leads to a rock-filled soakaway pit, so that spilled water never turns the collection area to mud. It is built for spills and drips: a tap left open for 8 hours passes about 9,504 liters, far more than a 1 cubic meter soakaway can absorb, so a pad does not replace a tap that closes.
Part of Community Water System
A drainage pad is the sloped concrete surface around a standpipe that keeps users’ feet and containers out of mud and carries spilled water to a drain and soakaway.
A Pad Keeps Mud, Mosquitoes And Contamination Away From The Water People Carry Home
Without a pad, spilled water collects around the tap, softens the ground and breeds mosquitoes, and containers set down in the mud pick up faecal bacteria that go into the water people carry home. The community water system page requires a concrete drainage pad 1.5 m × 1.5 m, sloped away from the tap, a drainage channel leading away, and a soakaway pit at the end.
What You Need
- Cement, sand and gravel for 0.225 m³ of concrete
- Formwork, boards for the edges
- A level and a straight board
- Rock to fill the soakaway pit
- A pipe or open channel from the pad edge to the pit
- A site well away from wells, springs and latrines
Method: Base, Slope, Pour, Drain
Step 1: Compact the base and set the formwork so that the pad surface will fall 2% away from the tap in every direction. Two percent is 2 cm per meter.
Step 2: Pour the concrete 10 cm thick, working it to the slope with the straight board and level. Smooth the surface so water runs instead of ponding.
Step 3: Cure it damp for several days (Concrete Curing). A pad that dries too fast cracks, and a crack holds water.
Step 4: Cut or lay the channel from the lowest edge to the soakaway with a continuous fall.
Step 5: Fill the soakaway pit, 1 m × 1 m × 1 m, with rock and cover it with flat stones (Soakaway). Overflow beyond what the pit absorbs needs a surface route (Drainage Design).
Step 6: Test it. Run the tap and watch where the water goes. The surface should drain with no puddles, and the channel should carry the flow without overtopping.
Worked Example: What The Soakaway Can Take
- Pad concrete volume = 1.5 × 1.5 × 0.10 = 0.225 m³ = 225 L.
- Fall across the pad: if the tap stands at the middle, the edge is 0.75 m away, and 0.75 × 0.02 = 0.015 m = 1.5 cm lower.
- A rock-filled pit of 1 m³ has voids of about 0.4 m³ = 400 L (Drainage Design uses this figure).
- A tap open at 0.33 L/s fills those voids in 400 ÷ 0.33 = 1,212 s, about 20 minutes.
- A tap left open for 8 hours passes 0.33 × 3,600 × 8 = 9,504 L, about 24 times the void volume.
So the pit absorbs the ordinary spill of a day’s use and a short mistake, not an overnight flow. The remedy for a tap left open is a tap that closes itself or a locked valve and a rule, not a bigger pit.
Common Mistakes
- A pad that is flat or slopes toward the tap. Water ponds round the pipe.
- A soakaway beside a well, spring or latrine. The spill carries contamination into them.
- Cracked, uncured concrete. Water collects in the cracks.
- A channel with no continuous fall. Water stands in the dips.
- Treating the pit as unlimited. In slow soil it fills quickly.
Safety
Wet cement burns, and an unshored pit can collapse
Wet concrete is alkaline and burns skin and eyes: wear gloves and eye protection and wash splashes off at once. Do not work in a deeper pit with unsupported walls. Keep the pad surface rough enough to be safe underfoot when wet, and clear in frost, because ice on a pad is a fall hazard.
What’s Next
- Learn next: Standpipe Construction — building the tap stand on the pad
- Combine with: Soakaway — sizing the pit for the soil