Take water out of a cistern with a tap if the tank is above ground, a hand pump if it is underground, or a siphon started with a priming pump, and never with a bucket, because every dipped bucket brings in dirt and bacteria. A suction hand pump lifts water about 6–7 m in practice, which is more than twice the depth of the 2.5 m example cistern.
Part of Cisterns and Rainwater Storage
Water extraction is the means of getting stored water out of a cistern while keeping the tank sealed. The method has to suit the tank’s position, and each one avoids opening the water to hands, ropes and buckets.
The Outlet Is A Contamination Point Too
A cistern is cleaned at the inlet and sealed at the roof. The outlet is the last open door. If people reach in with buckets, hands and ropes, they undo the work of the screen, the diverter and the lid. The three ways to draw water without opening the tank:
| Method | Works when | Page |
|---|---|---|
| Gravity tap | The tank is above ground or elevated | Gravity Tap |
| Hand pump | The cistern is underground | Hand Pump |
| Siphon | The outlet can be below the water level | below |
Siphon. Fill a hose, close both ends, put one end in the tank and the other below the water surface outside, and open both. Gravity then keeps it flowing, but only while the outlet is lower than the water level in the tank. The cisterns page starts it with a priming pump. Do not start it by mouth: you may swallow the water, and it puts the bacteria of your mouth into the tank. A siphon stops when the tank level reaches the outlet height or when air enters the hose.
What You Need
- A tap and fittings, or a pump, or a hose and priming pump
- A clean container for collecting — set under the spout, not into the tank
- A cover on the hatch, locked
Method: Choose The Method By Where The Tank Is
Step 1: Look at the tank. Above ground or on a hillside: fit a tap. Underground: fit a pump. A tank with neither: use a siphon until you can fit one.
Step 2: Fit the outlet before the first fill, not afterwards.
Step 3: Keep the hatch shut and locked. Open it only for inspection.
Step 4: Collect into a clean, covered container.
Worked Example
The 5,000 L tank has its tap 10 cm above the floor, so the last 10 cm cannot be drawn: π × 0.8² × 0.10 = 0.201 m³ = 201 L, about 4% of the tank, stays behind as a sediment reserve. A 2.5 m deep underground cistern needs a pump lift of about 2.5 m plus the height of the pump above the ground, comfortably within the 6–7 m suction limit, which is more than twice the cistern’s depth.
Common Mistakes
- A bucket “just this once”. It undoes the whole system (No Bucket Dipping).
- A siphon whose outlet is above the water. It will not run.
- A tap at floor level. It draws sediment.
- Leaving the hatch off. Animals, children and insects enter.
Safety
Never climb into a cistern to fix an outlet
A roofed cistern can hold air short of oxygen, and carbon dioxide or hydrogen sulphide pooled at the bottom. The commonest fatality pattern is a second person climbing in after the first collapses. Fix outlets from outside where possible. If someone must go in, ventilate at two openings, use a harness tied to a line held by an attendant, and keep a second person outside who pulls the line and never climbs in. Do not test the air with a flame.
What’s Next
- Learn next: No Bucket Dipping — why the bucket habit is the main threat
- Combine with: Hand Pumps — building a suction or force pump