How High Should Pool Water Be?
Keep the water about halfway up the skimmer opening. Pentair's skimmer guide says never to let it get within 1 inch of the top or bottom of that opening, because air can then get into the pump.
On this page (9 sections)
The target: halfway up the skimmer opening
The skimmer is the box in the pool wall that pulls surface water into the pump. Its opening, called the mouth, has a flap (weir) that lets water in and keeps debris from floating back out. The pump only works well when the mouth is part full.
Pentair's skimmer installation guide puts it plainly: maintain the water at approximately halfway up the skimmer opening, and keep it at least 1 inch away from both the top and the bottom edge. If the level drops too far, the guide warns, air might enter the hydraulic system. Your own pool or skimmer manual comes first if it says something different.
Pools without a skimmer in the wall, such as many inflatable and frame pools, have their own maximum fill line or a clip-on skimmer. Use the line in your manual. Intex's frame pool manual, for example, tells owners to drain rain water at once if it pushes the level above the maximum.
Level guide by situation
| Situation | Level | Source |
|---|---|---|
| Normal swim season, skimmer in the wall | About halfway up the skimmer opening; never within 1 in of the top or bottom of it | Pentair skimmer guide |
| After a storm, once the ground dries | Back to mid-tile or halfway up the skimmer | UF/IFAS Extension |
| Closed for winter, mesh safety cover | 12–18 in below the skimmer | Hayward |
| Closed for winter, solid or floating cover | 3–6 in below the tile | Hayward |
| Above-ground frame pool with a maximum line | At or below the line in the manual; drain rain above it | Intex manual |
Hayward adds that some covers do not need the water lowered at all, so check your cover's instructions. For the full closing routine, see how to close an inground pool and how to close an above-ground pool.
What happens when the level is too low
When the water falls below the skimmer mouth, the pump starts pulling air instead of water. Pentair's skimmer guide says low water can damage the pump through loss of prime. It adds that air pulled in by the skimmer can be trapped in the filter tank, which it calls a possible safety hazard.
Signs the level is too low:
- The skimmer makes a gurgling or sucking sound, or the water swirls into it like a drain.
- Air bubbles shoot out of the return jets.
- The pump basket will not stay full of water, or the pump loses prime.
- The water line sits below the weir, so the skimmer stops skimming.
Pentair's advice if the skimmer regularly sucks air is to raise the water level or call your pool service. Some skimmers have an equalizer line that keeps the pump supplied from the main drain when the level drops. That is a safety backup, not a way to run the pool low. Pentair says not to allow flow through the equalizer for long periods.
If the level is lower every day, evaporation may not be the whole story. The Intex manual lists a chronic low water level, lower than the day before, under leaks: a hole in the liner or hoses. Use the bucket test in the hot weather guide to compare evaporation with a leak.
What happens when the level is too high
A level above the skimmer mouth is less harmful to the pump but still a problem. The weir cannot move, so floating leaves, pollen, and oils slide past the skimmer instead of into it. Oils then stay on the tile, which is how a scum line gets worse. Very high water can also run into the skimmer lid, deck drains, or, in an above-ground pool, over the top of the wall.
After heavy rain, lower the water back to the normal level and no further. The Florida Swimming Pool Association says after a storm to drain the pool only down to its normal level. Partly draining an inground pool when the ground is soaked is a risk, because groundwater can push on an empty or low shell. Chemistry after rain is covered on the pool after rain page.
How many gallons is one inch?
You do not need a pool volume to top off a pool. You need the surface area. One inch of water over 1 square foot is about 0.62 gallons (7.48 gallons per cubic foot, divided by 12). Multiply that by your surface area in square feet.
| Pool | Surface area | Gallons per inch |
|---|---|---|
| 12 ft round | 113 sq ft | 70 |
| 15 ft round | 177 sq ft | 110 |
| 18 ft round | 255 sq ft | 159 |
| 24 ft round | 452 sq ft | 282 |
| 12 × 24 ft rectangle | 288 sq ft | 179 |
| 16 × 32 ft rectangle | 512 sq ft | 319 |
| 20 × 40 ft rectangle | 800 sq ft | 499 |
Rectangular pools with rounded corners hold a little less than the table shows, and free-form pools need a rough area estimate. Get your own size from the round pool calculator or the pool volume calculator. To see what the water costs, use the pool fill cost calculator.
Example: an 18 ft round pool at the typical summer evaporation range of 0.25 to 0.5 inch a day (Orenda) loses roughly 40 to 80 gallons a day. A full week at the top of that range is about 3.5 inches, or about 555 gallons.
How to add water
- Check the level at the skimmer. Note where it sits against the mouth, or mark the wall with tape.
- Run a hose to the pool and put the end in the water or over the edge. Set a timer, because a pool overfills faster than most people expect.
- Stop when the water is about halfway up the skimmer opening.
- Run the pump, then test free chlorine, pH, and alkalinity. Fresh fill water dilutes the chemicals a little and brings its own minerals. Evaporation takes only water and leaves stabilizer, calcium, and salt behind, so these build up over a season (Orenda).
If your fill water comes from a well, test it for metals first. See filling a pool with well water.
How to lower the water
- Check your local rules for where pool water may go. Intex's manual says to check local regulations for disposal.
- Turn off the pump. Use a submersible pump, or set a sand or cartridge filter's multiport valve to Waste if your manual allows it.
- Lower the level slowly and check often. Stop at the skimmer midpoint, or at your cover's winter level.
- Do not drain below the normal level when the ground is saturated, unless a pool professional says it is safe.
Do not run the pump while the water is below the skimmer mouth. Turn it off, add water, then restart it.
FAQ
How high should the pool water level be?
About halfway up the skimmer opening. Pentair's guide says to keep it at least 1 inch from the top and bottom of the opening.
Can the pool water be too high?
Yes. Above the skimmer mouth, the skimmer can no longer pull in surface debris and oils. It can also overflow or flood the skimmer lid. Lower it back to the middle of the opening, and no lower.
What happens if the water level is too low?
The skimmer pulls air, the pump can lose prime, and Pentair says that can damage the pump. Turn the pump off and add water.
How much should the water level drop each week?
Orenda gives 0.25 to 0.5 inch a day for an outdoor pool in summer, which is up to 3.5 inches a week. Much more than that, or a drop in cool weather, is worth a leak check.
Do I lower the water for winter?
It depends on your cover. Hayward lists 12 to 18 inches below the skimmer for a mesh safety cover and 3 to 6 inches below the tile for a solid or floating cover, and says some covers need no change.
Sources
- Pentair, Bermuda vinyl skimmer installation and user's guide (water level, 1 inch rule, air in the system): pentair.com PDF
- Hayward, Ten essential steps to closing your pool (winter levels by cover): hayward.com
- Intex, Metal frame pool owner's manual (excessive rain, chronic low water level): PDF
- Orenda Technologies, Evaporation and accumulation (0.25–0.5 in per day): blog.orendatech.com
- UF/IFAS Extension, Pools and hurricanes (post-storm level): ifas.ufl.edu
- Florida Swimming Pool Association, Hurricane preparedness (drain to normal level only): fspa.com