How to Drain a Pool With a Garden Hose (Siphon Method)
Updated June 11, 2026
Sometimes the only fix for pool water is to take some out and put fresh water back — cyanuric acid that’s climbed too high, salt or calcium you can’t get down any other way. None of those need fancy equipment: a garden-hose siphon drains water for free, using nothing but gravity. Here’s exactly how to do it — and the one rule that keeps a drain from turning into a five-figure repair.
How a garden-hose siphon works
A siphon moves water uphill and over the pool wall without any pump. Fill a hose completely with water, keep one end submerged in the pool, and run the other end to a spot lowerthan the pool’s surface. Because the long “downhill” side of the hose outweighs the short side inside the pool, gravity drags the whole column along and pulls pool water out behind it — and it keeps going on its own until you break the chain by letting air in or raising the outlet.
Step by step
The whole job is seven steps. The two that matter most: kill the pump’s power first, and get all the air out of the hose so the siphon actually catches.
Cut the power at the breaker
Flip the pump breaker off — not just the timer — before you start. As the water level drops, a running pump can suck air and run dry, which burns up the seal and motor. Killing power also keeps you safe while you’re working around water.
Mark your stop line
Decide how much to remove and mark the target level (a strip of tape on the tile works). Most reasons to drain — high CYA, salt, or calcium — only need a partial drain; our CYA, salt, and calcium calculators turn your target into exact gallons. Never plan to empty it (see the warning below).
Run the hose downhill to a legal spot
Lead the far end of the hose downhill to where it’s legal to discharge — usually a sewer cleanout, not a storm drain, the street, or a neighbor’s yard. Pool water often must be dechlorinated first. The outlet has to end up lower than the pool’s surface for the siphon to pull.
Fill the hose and submerge it to start the siphon
This is the whole trick: get every bubble of air out of the hose, then keep one end underwater. Easiest way — sink the entire hose in the pool until it fills completely, cap the outlet end with your thumb, then carry that capped end down below the water line and let go. (Or fill it from a spigot, then move it fast.) Never start a siphon by mouth on pool water.
Let gravity do the work
Once water is flowing it keeps itself going — no pump, no power. A garden hose only moves a few hundred gallons an hour, so a partial drain usually takes a few hours. Check on it; don’t walk away for the day.
Stop at your mark
When the water reaches your tape line, break the siphon: lift the pool end of the hose up out of the water (or pinch/cap it). Flow stops the moment air gets in or the outlet is no longer below the surface.
Power back on, refill, and re-test
Turn the breaker back on, top the pool back up to its normal level, and re-test. A partial drain dilutes everything at once — CYA, salt, calcium, and alkalinity all drop together — so rebalance from a fresh set of readings.
The one rule: never fully drain it (the “concrete boat”)
An in-ground pool is held in place mostly by the weight of the water in it. Take that water away and the empty shell behaves like a boat — and the “water” it can float on is the groundwater in the soil around and beneath it. After rain, in a high water table, or in clay soils that hold moisture, the pressure under an empty shell can be enough to crack it, heave it, or pop it partway out of the ground. Plaster pools lift and crack; fiberglass shells float; vinyl liners shrink, wrinkle, and tear once they dry out.
That’s why every reason covered here uses a partial drain — you’re only ever swapping a portion of the water, and the pool stays safely weighted the whole time. If you genuinely need to empty a pool (a full re-plaster, a liner change), that’s a job for a pro who can manage the water table and a hydrostatic relief valve, in dry conditions — not a garden-hose weekend project.
How much should you drain?
Dilution is proportional: swap half the water and you roughly halve whatever you’re chasing down. The exact amount depends on your current level and target, so let the calculators do it — the CYA calculator (the usual reason to drain), the salt calculator, and the calcium hardness calculator each turn your numbers into the gallons to drain and replace. Mark that level on the tile, siphon down to it, refill, and re-test.
Common questions
Do I have to turn off the pump to drain my pool?
Yes — switch the pump off at the breaker first. A garden-hose siphon works entirely on gravity and doesn’t use the pump at all, and if the pump keeps running while the water level falls it can suck air and run dry, which damages the seals and motor. Turn it back on once you’ve refilled to the normal level.
How do I start a siphon with a garden hose without sucking on it?
Submerge the whole hose in the pool so it fills completely with water and all the air escapes. Cap the outlet end with your thumb (or a valve), carry that end below the pool’s water level, and let go — gravity takes over. Alternatively, fill the hose from a spigot, then disconnect and drop one end in the pool. Never start a siphon by mouth on pool water; it’s chemically treated.
How long does it take to drain a pool with a garden hose?
A standard garden hose only siphons a few hundred gallons per hour, so it’s best for partial drains. Dropping a 20,000-gallon pool by, say, a third (about 6,500 gallons) can take much of a day. Running two hoses, using a wider hose, or a submersible pump speeds it up — but for the partial drains pool chemistry needs, a single hose overnight is usually fine.
Can I drain my pool all the way to clean it?
Not without serious risk, and not as a DIY siphon job. An empty in-ground pool can be pushed up, cracked, or floated out of the ground by groundwater pressure — the “concrete boat” effect — and vinyl liners shrink and shift when dry. Full drains should be done by a professional who can manage the water table and a hydrostatic relief valve, ideally in dry conditions. For chemistry fixes you only ever need a partial drain.
Where can I drain pool water?
Check your local rules first — many areas require pool water to be dechlorinated and sent to the sanitary sewer (a cleanout), not a storm drain, street, or waterway, because chlorine harms aquatic life. Don’t flood a neighbor’s property. When in doubt, stop chlorinating for a few days first so the water can be discharged safely, and follow your municipality’s guidance.
How much water do I need to drain to lower CYA (or salt/calcium)?
Dilution is proportional: replacing half the water cuts CYA, salt, or calcium roughly in half. To go from 100 ppm CYA to 50, you’d swap about half the pool; to go from 100 to 70, about 30%. Our CYA, salt, and calcium calculators do this exactly — enter your current and target level and they give you the gallons to drain and replace.
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