When you actually need to drain
The common reasons are chemistry you cannot fix by dosing, mainly high cyanuric acid or high total dissolved solids, and repairs or resurfacing. For chemistry, you rarely need a full drain; replacing part of the water dilutes the problem. To halve your CYA, for example, you replace about half the water, which the cyanuric acid calculator context explains.
So before draining the whole pool, ask whether a partial drain solves it. It usually does, and it avoids the bigger risks.
The risks of a full drain
An empty inground pool is dangerous in two ways. Groundwater pressure under the shell, called hydrostatic pressure, can push an empty fiberglass or concrete pool up out of the ground, especially after rain or with a high water table. And a vinyl liner that dries out can shrink and crack, so it may not fit when you refill.
Because of this, do not fully drain an inground pool casually. If you must, it is often a job for a professional who can relieve hydrostatic pressure through the relief valve. Above-ground pools do not have the float risk but can still damage a liner if left empty in the sun.
How to do it
For a partial drain, a submersible pump is the usual tool: drop it in, run the discharge hose to where the water can legally go, and pump down to the level you need. Watch it so it does not run dry. For lowering before winter or a small refresh, this is straightforward.
Know where the water is allowed to go before you start. Many areas require draining chlorinated or saltwater to the sanitary sewer through a cleanout rather than the storm drain or a neighbor's yard, and salt water can kill plants and lawn. Check your local rules.
Refill and rebalance
After a partial drain, top back up and rebalance, since fresh water changes your numbers. Reset alkalinity and pH, recheck calcium hardness, and bring chlorine back to target with the chlorine calculator. If you are unsure of the new volume, the pool volume calculator helps.
Frequently asked questions
How do I drain my pool?
For a partial drain, use a submersible pump with a discharge hose run to where the water can legally go, and pump down to the level you need without letting the pump run dry. Avoid fully draining an inground pool casually because of float and liner risks. After draining, top up and rebalance the water.
Is it safe to drain a pool completely?
Not without care. An empty inground pool can be pushed out of the ground by groundwater pressure, and a vinyl liner can shrink and crack when dry. Full drains are best left to a professional who can relieve hydrostatic pressure. Most chemistry problems are solved with a partial drain instead.
Why would I need to drain my pool?
Usually to fix chemistry you cannot dose your way out of, mainly high cyanuric acid or high total dissolved solids, or to make repairs or resurface. For chemistry, a partial drain that replaces some of the water is almost always enough and far safer than emptying the pool.
Where can I drain my pool water?
Check local rules first. Many areas require chlorinated or salt water to go to the sanitary sewer through a cleanout, not the storm drain. Salt water also damages lawns and plants. Never assume; draining to the wrong place can violate local regulations and harm landscaping.
Can I drain my pool to lower cyanuric acid?
Yes, and a partial drain is the reliable way to lower CYA, since no chemical removes it well. Replace water in proportion to how much you want CYA to fall: roughly half the water to halve CYA. You do not need to fully drain the pool to do it.