Drainage design for a standpipe is planning where every drop of spilled and waste water goes: a pad sloped 2% away from the tap, a channel from the pad edge to a soakaway pit, and a pit large enough for the water it will actually receive. A tap left running at 0.33 L/s sends 1.2 m³ an hour, which fills the open space in a 1 m³ rock-filled pit in about 20 minutes, so self-closing taps and a second overflow route matter as much as the pit size.
Part of Water Distribution
Drainage design for a water point is the layout of slopes, channels and absorption pits that carry away water spilled at a tap. Poorly drained standpipes produce mud, mosquitoes and contaminated ground.
The Normal Spill Is Small, But The Worst Case Is Not
Most of the water at a standpipe goes into containers; a little is spilled while filling, rinsed off feet, or dripped. Size the drain for the normal case, then check what an accident does.
For a standpipe serving 8 households, assuming 5 people each (an assumption) and 20 L per person per day: 8 × 5 × 20 = 800 L/day through the tap. If 10% is spilled (also an assumed share), the drain gets 80 L/day, a trivial load.
The worst case is a tap left open. A bucket test of 20 L in 60 s gives 0.33 L/s, which is 0.33 × 3,600 = 1,200 L/h = 1.2 m³/h. A 1 m³ pit filled with rock has voids; with an assumed 40% open space, that is 0.4 m³ = 400 L. At 1.2 m³ an hour it fills in 0.4 ÷ 1.2 = 0.33 h = 20 minutes, ignoring what soaks away. After that the water comes out across the ground.
What You Need
- A pad sloped 2% from the tap (Standpipe Construction)
- A channel, open or piped, with a continuous fall
- A soakaway pit (Soakaway) on ground that drains, downhill of the standpipe and away from wells and latrines
- A second route for overflow: a shallow ditch to a safe place
- Self-closing taps where waste is a risk (Tap Types)
Method: Slope, Channel, Pit, Backup
Step 1: Lay out the fall. From tap to pad edge to channel to pit, the surface must always drop.
Step 2: Check the route for places where water can pool, and fill them.
Step 3: Size the pit for the normal load and test the soil’s drainage.
Step 4: Add the backup route for a tap left open.
Step 5: Walk it in the rain and fix what ponds.
Common Mistakes
- Sizing only for the average. The accident case floods it.
- A channel with a dip. Standing water breeds mosquitoes.
- Draining toward the tank, a house or a well. Dirty water must go away from all three.
- Sending greywater or sewage into the standpipe soakaway. It is for clean spill water only.
- Never cleaning the channel. Silt and weeds block it.
What’s Next
- Learn next: Winterization — what freezing does to a standpipe and its drain
- Combine with: Flood Control and Drainage — managing water at a larger scale