How Far Should You Drain Your Pool for Winter?

Matching Winter Water Levels to Your Cover Type

The type of cover you place over your pool determines how much water you need to drain. Many pool owners assume that every pool follows the same rule, but your cover works directly with the water underneath it. If the water level sits too high, freezing ice can shift against the cover edges or creep into the skimmer (the surface suction opening in the pool wall). If the water sits too low, winter storms can tear your cover or pull its mounting anchors out of the patio deck.

Solid winter covers, including standard vinyl tarps held down by water bags and solid safety covers secured with brass deck anchors, require the water to stay relatively high. You should lower the water level 4 to 6 inches below the bottom edge of the skimmer mouth. Solid covers do not let water seep through. When heavy snow, sleet, and rain collect on top, the cover sags downward until it rests on the water below. The pool water acts like a solid floor that supports thousands of pounds of winter precipitation. If you drain the pool a foot or two down, a heavy snowstorm can rip the cover material, bend the deck hardware, or drag heavy water bags directly into the deep end.

Mesh safety covers require a noticeably lower water line before you pack away your equipment. You should lower the water level 12 to 18 inches below the skimmer mouth. A mesh cover behaves like a giant kitchen strainer stretched across your yard. It blocks falling leaves, pine needles, and windblown debris, but it lets all rain and melted snow pass directly into the pool. Over a normal winter, snowmelt will gradually fill the pool back up. If you start with the water just a few inches below the skimmer, autumn storms will raise the pool level within weeks. Once that happens, dirty water will push back up through the mesh fabric, soaking sitting leaves and turning your clean pool into a messy swamp before spring arrives.

If you use an automatic safety cover, you must follow the builder guidelines closely. Most automatic cover systems run along metal tracks beneath the deck coping stones. These systems generally need the water level to stay just 2 to 4 inches below the skimmer opening. Automatic cover vinyl does not stretch well, and letting the water drop more than a few inches can pull the sliders completely out of their tracks under the first winter freeze.

Why You Should Never Empty a Pool Completely

Draining a pool completely dry is the fastest way to ruin it. It is easy to think that getting rid of every drop of water guarantees you will avoid cracked pipes or ice damage. In reality, an empty pool is extremely fragile. The water inside your pool does not just give you a place to swim. It provides continuous physical weight that keeps the pool structure stable against the heavy, shifting earth around it.

The biggest hidden threat under your lawn is hydrostatic pressure (underground water in the dirt pushing against the pool shell). Soil absorbs water from autumn rainstorms, underground springs, and melting snow. Saturated dirt behaves like liquid mud, pressing inward against the pool walls and upward against the floor. A typical backyard pool weighs tens of thousands of pounds when full, which easily counteracts this outward force. Once you empty that water, the pool becomes an open bowl sitting in a wet ditch.

Underground water pressure can literally lift an empty concrete or fiberglass pool out of the earth like a boat rising on a lake. Once a pool shifts, pops upward, or breaks away from the deck, it will never sit level again. The plumbing underground snaps, the concrete deck cracks in half, and fixing the problem often requires completely demolishing the pool with heavy machinery. Even if the shell does not lift out of the ground, freezing soil can bow fiberglass walls inward or fracture thick concrete floors.

Emptying a pool is just as catastrophic for vinyl liners. Water weight is the only thing that holds the vinyl sheet tightly against the pool walls and floor. When you pull the water out, the liner loses its hold. Cold winter air causes the vinyl to contract and shrink quickly. Once a liner shrinks, it will pull out of its upper track, wrinkle across the bottom, and rip apart when you try to refill the pool in the warmer spring months.

Water Depth Limits for Vinyl, Fiberglass, and Concrete

Your pool construction sets a strict boundary on how far down you can safely lower the water line. Different materials react differently to cold air, shifting soil, and moisture loss. Checking your pool build before you pump out water prevents expensive structural damage.

Vinyl liner pools must always keep water resting across the entire shallow end. If you drain a vinyl pool below the shallow floor, the liner will pull away from the pool steps, corner seams, and wall fittings. Groundwater running under the floor can float the loose liner, creating large water pockets and permanent wrinkles that never smooth out. Keeping your water at the right height protects the material, which is a major factor in how long vinyl pools and liners last over the seasons. Never drop the water line lower than one foot below the skimmer in a vinyl pool unless you are using a commercial air blower to blow out lines that sit deeper in the wall.

Fiberglass pools have flexible shells that depend heavily on internal water pressure to keep their factory shape. Fiberglass does not expand or contract at the same rate as the gravel or sand packed around it. If you drain a fiberglass pool more than a foot below the skimmer opening, damp winter dirt can press the side walls inward, cracking the gelcoat finish or bulging the walls permanently. Many fiberglass manufacturers will void their structural warranties if you drain the water lower than the bottom of the skimmer mouth.

Concrete, gunite, and plaster pools can tolerate lower water levels than vinyl or fiberglass, but they bring their own set of seasonal problems. Plaster finishes must stay damp. If you lower the water line too far and leave the bare plaster exposed to dry, freezing winter winds, the finish can develop tiny cracks, peel, or chip away from the masonry. Repairing that kind of wall damage involves significant work, and understanding how much it costs to resurface a pool will convince any owner to protect their plaster surface during winter. You also need to keep the water below the waterline tile border if you live in an area with hard freezes. Water that freezes against ceramic tiles can expand behind the grout and pop the decorative tiles right off the concrete wall.

Safe Draining Steps, Pipe Protection, and Winter Monitoring

Lowering your pool water does not require commercial equipment, but you must take your time and follow the right sequence. Rushing the process or running the wrong equipment can damage your pool pump or drain the water too far before you notice.

1. Clean the pool floor and skim out floating leaves so you do not suck debris into your filtration equipment while lowering the water line.
2. Turn off the pool heater, salt cell system, and automatic chemical feeders to prevent heating elements from running dry.
3. Connect your waste hose to your pool filter. Turn the multiport valve on your filter to the "Waste" setting rather than "Backwash." The waste setting pumps water straight out of the pool without forcing dirt through the sand or glass media in your filter tank.
4. If your water level needs to drop below the skimmer opening and your pool lacks a working main drain on the bottom floor, shut off the main pump. Lower a small electric utility pump or submersible pump into the shallow end of the pool and run a standard garden hose out to a safe drainage spot.
5. Monitor the water line closely as the pump runs. Check the distance from the bottom rim of the skimmer opening down to the water surface using a standard tape measure. Turn off the pump as soon as you hit your target depth for your specific cover.

Once the water sits at the right winter depth, you must seal the openings in the pool wall so you do not have to drain the pool all the way to the floor. Use this quick checklist to protect your pipes and wall openings before freezing temperatures arrive:

• Clear water out of the plumbing by using an air blower or shop vacuum on the pipes at your equipment pad.
• Insert a winterizing plug (an expanding rubber or threaded stopper that seals pipes against freezing) tightly into each return jet (the wall nozzle pushing clean water into the pool).
• Screw a hollow freeze guard tube or collapsible foam bottle into the bottom pipe opening inside the skimmer to absorb the force of expanding ice.
• Pour non-toxic swimming pool antifreeze into the plumbing lines if you live in an area where ground freezes run deep into the soil.
• Remove the small drain plugs on the bottom of your pool pump, filter tank, and heater header so lingering moisture drains out completely.

Your job does not completely end once the cover snaps into place. Winter brings changing weather, and rain or snow will steadily alter the water level under your cover. If you have a solid cover, melted puddles will collect on top of the fabric. Use a small cover siphon or an automatic cover pump to remove that surface water before it gets heavy enough to drag the cover down. If you have a mesh cover, peek under the edge once a month. If winter rain fills the pool back up to the bottom of the skimmers, use your submersible pump to lower the water back down to its safe winter depth.

FAQs

Do I need to drain pool water below the return jets?

You do not need to drain the water below the return jets if you clear the lines with air and plug them tightly. Use an air blower or vacuum to push all water out through the return jet nozzles, then screw in a rubber or threaded winterizing plug while air is still bubbling out. This keeps the underground pipes completely dry without forcing you to drain extra feet of water out of the pool shell.

What happens if rain and snow refill the pool during winter?

If rain and melting snow raise the water level back into the skimmer opening, freezing weather can crack the skimmer plastic. Mesh covers let water through continuously, which often causes the pool level to rise several inches by mid-winter. Keep an eye on the water level every few weeks and use a small submersible pump to drop the water back down if it reaches the skimmer frame.

Can freezing water crack my skimmer if the water level rises back up?

Freezing water will crack a plastic skimmer if there is no room for the expanding ice to move. Water expands by roughly nine percent as it turns to solid ice, which exerts immense pressure on plastic walls. Threading a hollow plastic freeze guard tube into the skimmer suction port prevents this damage by collapsing inward under ice pressure, protecting the outer housing even if water rises back inside.