An empty pool feels like the safe option. The wall is designed to push inward, and the water is what pushes back.

Lower the level. Never drain it

The rule that saves the pool, and the mechanism is what makes it stick. A manufacturer states it directly: you can lower the water level but never drain it, because once the water of an above-ground pool drains there is no way to keep the walls in place, since they are designed to thrust inward against the force of the water within. So the water is opposing a structure that is trying to move, and taking it away removes the only thing balancing it. Others describe the outcome rather than the cause, noting that an above-ground pool needs the weight of the water for stability and that an empty pool can collapse, with wind and snow doing the rest. Draining is the one winterizing decision that can cost the whole pool.

Do not lower it as far as you can either, and the sources disagree about how far

This is a window rather than a direction, which is easy to miss when every guide says to lower the water. One source says four to six inches below the skimmer. Another says about three inches below the mouth of the skimmer and warns explicitly not to lower the level too much, because doing so can add stress to the wall, the liner and the fixtures. A third distinguishes pool types: four to six inches below the skimmer for an inground pool, but for an above-ground pool, reduce the level to just below the return line fitting, on the basis that above-ground skimmers sit higher on the wall and the flexible liner can accommodate some ice movement. Those are three different answers from three reputable sources, so use your pool manufacturer’s figure and treat "as low as possible" as wrong.

The skimmer failure is a hanging weight, not a crack

The most specific and least expected failure mechanism in this category. The assumption is that a skimmer breaks because water freezes inside it and expands, which does happen. The described mechanism is worse: the skimmer catches water which then freezes, causing the skimmer to become too heavy for the wall to support, and this eventually causes the walls to collapse. A block of ice in the skimmer body becomes dead weight hanging off thin steel. That reframes what lowering the water is actually for. It is not only about protecting the skimmer as a component, it is about not allowing a weight to form there in the first place, which is also why a skimmer faceplate cover is a legitimate alternative to draining.

A skimmer plate lets you skip lowering the water, and it helps the cover too

A winter skimmer cover is a plate that seals the skimmer opening completely, letting you drain the skimmer plumbing without lowering the pool at all. That is worth knowing on its own, and there is a second benefit almost nobody mentions. Keeping the water at its normal level is better for the winter cover, because with a solid cover, draining below the return lines puts added pressure on the cover as rain and snow collect on top, and you end up pumping water off it to protect it. Water under a cover supports it. A cover spanning air over a lowered pool is carrying every pound of snow on its own fabric and its own fasteners.

The air pillow is an ice compensator, which explains what it is for

Its other name is the useful one. A pool air pillow is also called an ice compensator because it compensates for the pressure of snow and ice on top of the cover, and placing it under the cover protects both the sides of the cover and the walls of the pool. So it is not flotation and it is not a tent pole. It is a compressible volume that gives expanding ice somewhere to go, so that the ice pushes into the pillow rather than outward against the wall. That matters because ice expansion pushing against the walls is what causes them to buckle under the pressure and weight. Worth an honest note: one homeowner reports their pillow popped a few weeks into winter, the season ended without damage, and they stopped using one. That is one pool in one climate rather than a recommendation, and knowing what the pillow is for lets you weigh it.

Draining also costs you the liner, separately from the wall

Two different damages come from the same mistake and it is worth separating them. The structural one is the wall losing what balances it. The other is the liner: guidance notes that a vinyl liner can dry out, shortening its life considerably, and that a pool sitting empty can leave the liner dried out, shrunk or cracked. That is consistent with what liner suppliers say about vinyl being a material whose behavior depends on condition and temperature. So an empty pool over winter risks the structure and ages the single most expensive replaceable component at the same time, which is a poor return on the water you saved.

Air dry the hoses, and never use automotive antifreeze

Two equipment items that get skipped for different reasons. On hoses: disconnect them, let all the water run out, and let them air dry before storing them out of direct sunlight, because storing them wet is how you find mold in them next season. Draining is not drying, and the difference costs you an unpleasant hour in spring. On antifreeze: pool antifreeze is a real product, a propylene glycol formulation that protects against freeze damage without harming pool surfaces, and it is genuinely useful where lines cannot be fully cleared. Automotive antifreeze is not a substitute at any price. It is toxic and can damage pool equipment, and it is going into water people swim in.

Kill the power first, and plug the returns properly

Sequence and detail on the equipment side. Turn off all electrical power to the pool equipment at the circuit breaker before touching anything, which connects to the bonding and GFCI requirements covered elsewhere in this category. Then plug the return jets with threaded winterizing plugs, and there is a fit test worth using: plugs should seat snugly without requiring excessive force, quality ones include O-rings or gaskets, and each should be checked with a gentle pull to confirm it is secure. A plug that needed forcing is likely the wrong size and a plug that pulls out easily will let water into the line it was protecting. Drain the pump and filter fully and store the pump indoors, open the drain valves on a sand filter, and consider covering the multiport valve, since it is the part most exposed to ice.