How to Drain a Pool Safely: Methods, Rules and the Refill

Working out how to drain a pool means planning three jobs: getting the water out legally, keeping the shell in the ground while it's empty, and getting the water back in quickly. Most people plan the first and forget the other two. A concrete in-ground pool can be drained with the filter pump set to waste, a submersible pump or a siphon hose. A vinyl-liner or fiberglass in-ground pool shouldn't be drained at all without a pool professional, because an empty shell can float out of the ground and an exposed liner can shrink and tear.

Below is the procedure, including the hydrostatic valve step that helps keep a concrete pool from popping, where the water may go, and the refill to book before the first gallon leaves. We don't drain pools ourselves. You or your pool contractor handle that, and we handle the water coming back in.

Should you drain at all?

Most problems don't need an empty pool. A full drain is for:

• Cyanuric acid (stabilizer) so high that chlorine stops working well. Dilution is the only reliable way to lower CYA, and a partial drain often does it.
• Calcium or total dissolved solids so high that the water turns cloudy and scales.
• An acid wash, a replaster, a pebble finish or a new liner.
• Repairs to the main drain, lights, returns or the shell.

For a green, cloudy or stained pool, start with chemistry and filtration. For CYA, do the partial-drain math before committing to a full drain. Replacing a third of the water cuts CYA by a third, and going from 150 ppm to 50 ppm means replacing two-thirds of the pool, which on a 20,000-gallon pool is about 13,300 gallons out and 13,300 back in. When to drain a pool walks through each case with the thresholds.

Before you drain: weather, water table, permits

Watch the weather. Don't drain in the hottest part of summer or during a freeze. Direct sun on dry plaster can cause cracking and crazing, and an exposed vinyl liner shrinks. Pick a mild stretch of days and plan to refill as soon as the work is done.

Check the water table, because high groundwater is what pops pools. After heavy rain, or anywhere the ground stays wet a few feet down, groundwater pushes up on an empty shell. Wait for a dry spell, and if the pool has a hydrostatic relief valve, plan to open it (details below).

Discharge rules are local and vary a lot. Some cities want pool water sent to the sanitary sewer through the house cleanout, others prefer it spread on your own lawn, and some allow dechlorinated water into the street. Some also ask for a permit or a notice first. Check your city's wastewater or stormwater page before you start. Where to drain pool water lists the usual options and the ones that get you fined.

Shut off what you don't need. Switch the heater and chlorinator off at the breaker, and the pool pump too unless you're draining with it (Method 1). A pump that keeps running once the water drops below the skimmer can run dry and burn out its seal.

Book the refill. By hose at 5 to 10 gallons a minute, a 20,000-gallon pool takes 33 to 67 hours to refill, and by tanker it's 3 to 4 loads, usually done in a day. Spring openings and summer weekends book up first, so book the water before you drain. Our pool refill after drain service times the first load to your contractor's schedule.

Method 1: filter to waste through the main drain

This uses the pool's own pump. It's a quick option for a concrete pool with a working main drain and a multiport valve on the filter.

1. Close the skimmer valve so the pump draws only from the main drain. On most equipment pads this is a valve on the suction side, often labeled for the skimmer and main drain.
2. Set the filter's multiport valve to Waste (or Drain). Cartridge filters have no Waste setting, so unless your plumbing has a separate drain valve, use a submersible pump instead.
3. Run the waste line to a discharge point your city allows, such as a sewer cleanout or the yard.
4. Turn on the pump and watch the level drop. On Waste it moves water far faster than a garden hose, so a big pool comes down a long way in several hours. Slow it down if the cleanout backs up or the yard floods.
5. Stop when the pump starts to draw air. It loses suction before the main drain is fully uncovered, so expect some water left in the deep end, and switch to a submersible pump for the rest.

Never run the pool pump dry. If you hear it racing or see the strainer basket fill with air, shut it off at once.

Method 2: submersible pump

A submersible pump (a utility or sump pump, or a rented trash pump) is the standard tool for liner pools with no main drain, for finishing after Method 1, and for anyone whose pool pump can't be set to waste.

1. Attach a discharge hose to the pump outlet. A backwash hose or a 1.5 to 2 inch lay-flat hose moves far more water than a garden hose, and many small submersibles take either.
2. Lower the pump to the deepest point by its rope, not its cord, and keep the cord out of the water where you can.
3. Run the hose to the discharge point and plug the pump into a GFCI outlet.
4. Let it run. Small utility pumps are commonly rated around 1,800 to 3,000 gallons an hour with no lift and move less through a long hose, so a 20,000-gallon pool takes roughly 7 to 11 hours, often longer. A rented trash pump is several times faster.
5. Check the discharge every hour. A hose that pops off can flood your side yard or your neighbor's.
6. When the pump starts sucking air, lift it out. Sweep the last inch toward it or use a wet vac.

If you're only draining partway for CYA, mark the target level on the tile and stop there. A submersible suits that job because the skimmer and the pool pump stay out of it.

Method 3: siphon with a garden hose

It's the slowest method, but it needs no electricity and works for a partial drain or a small above-ground pool.

1. Put one end of the hose in the pool and fill the whole hose with water, either by submerging it or by running water through it from a tap.
2. Cap the far end with your thumb, carry it to a discharge point lower than the pool's water surface, and let go.
3. Keep the pool end weighted at the depth you want to drain to.

A siphon has only gravity pushing it, so it's slower than a hose filling from the tap, at about 2 to 6 gallons a minute (more with a short, wide hose and a big drop), and it stops once the pool's surface falls to the outlet's level. Dropping a 24 ft round above-ground pool a foot means about 3,400 gallons at 280 gallons per inch, so plan on roughly 9 to 28 hours with one hose. Several hoses together speed it up. Draining with a hose covers how to start the siphon without getting a mouthful.

Where the water can legally go and the hydrostatic relief valve

The details are local, but a few rules come up almost everywhere.

Dechlorinate first. For the yard or the street, cities generally want chlorine near zero and pH close to neutral, and the EPA's WaterSense guide suggests letting the water sit 48 to 72 hours with no chemicals added before using it on landscaping. Test before you drain and use a dechlorinator if needed. Acid-wash water should be neutralized and kept out of storm drains, which usually means the sanitary sewer.

Keep it out of storm drains unless your city says otherwise. They usually run to creeks and lakes untreated, which is why many cities fine for chlorinated or salty pool water there. Federal stormwater rules let a city allow dechlorinated pool water into its storm drains, and some do. Salt pool water usually has to go to the sanitary sewer, since salt harms lawns and plants. Never drain a pool into a septic system, and keep the water off your neighbor's land.

Now the valve. Many concrete pools have hydrostatic relief valves, either in the main drain sump or as threaded plugs in the floor, often plastered over. They let groundwater flow into the pool instead of lifting it. With water in the pool, its weight holds the shell down. Empty, only the shell's own weight holds it, and in wet ground that may not be enough.

Once the pool is nearly empty, find the valve (take off the main drain cover first) and unscrew or open it, and plan to fit a new one or reseal it before refilling. If groundwater flows up through the hole, the valve is doing its job. Leave it open, pump that water somewhere it won't run back under the pool, and get the pool refilled quickly. If nothing comes up, the ground is dry and you have some margin. Either way, don't leave the pool empty longer than the work needs. Hydrostatic pressure explains what a popped pool looks like and why there's no cheap fix.

Vinyl and fiberglass pools carry more risk. A fiberglass shell can float, a vinyl liner can lift or shrink, and many have no relief valve to open, so involve a pool professional before draining either.

How long it takes and how long it can sit empty

These rates are typical, so plan on the slow end.

Keep the time empty as short as you can. A plaster pool in mild, dry weather can sit a few days for repairs, but in hot sun or after heavy rain, plan the refill for the day the work finishes. A vinyl liner should be refilled the same day it's exposed, and a fiberglass shell shouldn't sit empty at all without the installer's go-ahead.

Planning the refill

The refill is where the timing and most of the cost sit. For an existing plaster finish, the usual routine is to fill to mid-skimmer and run the pump continuously for 24 to 48 hours, testing and balancing alkalinity, pH, calcium, stabilizer and chlorine once the water has mixed. Fresh plaster is different. It has to be filled continuously from the moment the crew says go, with a soft cloth over the hose end, and the builder's start-up sheet overrides this.

By hose, a 20,000-gallon pool is a day and a half to three days of running water, plus a sewer charge on the same gallons if your utility bills it. By tanker it's 3 to 4 loads, usually done the same day. On a well, a full refill runs the pump for a day or more, which is hard on pump and well alike.

A partial drain for CYA costs less either way. Replacing about 13,300 gallons is 2 to 3 loads, so measure how far down you went and the quote will have the right count. We ask before sending an extra load, and loads not yet dispatched when the pool is full aren't charged. The after-the-fill checklist picks up from the moment the water reaches the skimmer.

Frequently asked questions

Can I drain my pool completely?

A concrete pool, yes, with the hydrostatic valve opened and a refill planned within days. A vinyl-liner or fiberglass in-ground pool shouldn't be fully drained without a pool professional, because the shell can float and the liner can shrink. Above-ground pools can be drained fully, but the liner should be refilled the same day.

Can I drain pool water onto my lawn?

Sometimes. Some cities prefer dechlorinated, near-neutral water spread on your own lawn, and others don't allow it. Salt water harms grass and soil, so it usually belongs in the sanitary sewer. Check your city's rules, and don't let the water run onto a neighbor's property or into a storm drain where that's banned.

How far down should I drain for high cyanuric acid?

Work it out from the ratio you need. Dropping CYA from 120 ppm to 60 ppm means replacing half the water, so mark the halfway level, pump down to it with a submersible and refill. You don't need to empty the pool.

How long after draining can I refill?

As soon as the work is done. After a repair that's usually the same day, and after a replaster it's the moment the crew finishes, filled continuously. Book the water before you drain, so a truck or two hoses are ready when the pool is.

Does draining damage the pump?

Only if it runs dry. If you drain with a submersible, switch the pool pump off at the breaker before the water drops below the skimmer and leave it off until the water is back above mid-skimmer. If you drain with the pool pump on Waste, keep the skimmer valve closed and shut the pump off the moment it pulls air.

Once you know when the pool will be empty, tell us the gallons and the ZIP. We'll plan the refill loads and book our hauler for you, so the pool doesn't sit empty longer than it has to. Get your refill price.