Why lower the water at all?
Water left in the skimmer and in the return lines can freeze, expand and crack plastic fittings and pipes. Lowering the level below the skimmer opening, and blowing out and plugging the lines, keeps freezing water out of the parts that break. In regions without hard freezes, many owners keep pools running through winter and do not lower the water at all.
Common starting points
Your cover maker's and pool builder's instructions come first. These are commonly cited rules of thumb:
| Pool and cover | Typical water level for winter |
|---|---|
| In-ground pool, solid cover | A few inches below the skimmer opening, often about 4 to 6 in |
| In-ground pool, mesh safety cover | Lower, often around 12 to 18 in below the skimmer or tile, because rain and snowmelt pass through and refill the pool |
| Skimmer and lines winterized with plugs | Often little or no lowering needed; follow the plug maker's directions |
| Above-ground pool | Just below the skimmer and return, or not at all with a skimmer plug |
Never drain a pool completely
Do not empty a pool to winterize it. An in-ground pool can be pushed up out of the ground by groundwater when it is empty, and a vinyl liner can shrink, wrinkle or pull loose when the water that holds it in place is removed. The water in the pool also supports the cover and the walls through the winter. If you need to drain a pool for repairs, talk to a pool professional first.
How many gallons to pump out
Each inch of depth holds the water surface area × 1/12 ft of water. In gallons:
gallons per inch = surface area (sq ft) ÷ 12 × 7.48
gallons to remove = gallons per inch × inches to lower
In metric, each centimeter of depth holds the surface area in m² × 10 liters.
Worked example
A 40 × 20 ft in-ground pool has an 800 sq ft surface. Each inch holds 800 ÷ 12 × 7.48 = about 499 gallons.
| Lower by | Gallons to remove | Time at 30 gal per minute |
|---|---|---|
| 6 in | about 2,992 gal | about 1 hour 40 minutes |
| 12 in | about 5,984 gal | about 3 hours 19 minutes |
The 30 gallons per minute is only an example; check the flow rating of your own pump or use the filter's waste setting as your equipment manual describes. The whole pool, with 3.5 ft at the shallow end and 8 ft at the deep end, holds about 34,408 gallons. Get the figures for your pool from the pool volume calculator, which shows water per inch of depth.
For a round above-ground pool 16 ft across, each inch is about 125 gallons, so lowering it 4 inches removes about 501 gallons.
Lowering the level accurately
Before you start, put a piece of tape on the tile or wall at the target water level, measured down from the bottom of the skimmer opening. Check it as you pump so you do not overshoot. Remember that rain and snowmelt will raise the level again over winter, especially under a mesh cover, so check it through the season if your cover maker recommends it.
Where to send the water
Many towns regulate where pool water may be discharged, especially chlorinated or salt water. Common requirements include letting chlorine levels drop before draining and discharging onto your own lawn rather than into the street or storm drain. Check local rules, and keep discharge away from foundations, septic fields and neighbors' property.
A typical closing sequence
- Clean the pool, then test and balance the water using a reliable test kit.
- Add winterizing chemicals only as their labels direct, using your pool's volume.
- Lower the water to the level your cover and equipment instructions call for.
- Blow out the lines, plug the returns and skimmer, and drain the pump, filter and heater.
- Fit the cover securely and keep it free of heavy debris through winter.
Safety
Turn off power to the pump and other equipment at the breaker before working on it. Pool chemicals can react dangerously: never mix them, and add chemicals to water, not water to chemicals. A cover is not a walking surface, so keep children and pets away from the pool over winter, and remove standing water from a solid cover with a cover pump.
Frequently asked questions
How far below the skimmer should winter water be?
With a solid cover, a few inches below the skimmer opening is common. Mesh covers often call for a lower level. Follow your cover maker's instructions.
How many gallons is 1 inch of water in my pool?
Divide the surface area in square feet by 12 and multiply by 7.48. A 40 × 20 ft pool holds about 499 gallons per inch.
Should I drain my pool for winter?
No. Fully draining can damage liners and can lift an in-ground pool out of the ground. Lower the water only as far as your equipment and cover require.
Do the math for your own project.
Open the pool volume calculator