If you are currently standing on your deck squinting at the tile line and wondering where should pool water level be, the short answer is almost always halfway up the opening of your skimmer. It sounds like a small detail, but keeping that water line right in the middle of the skimmer mouth is the secret to a crystal-clear pool and a pump that doesn't burn out. Most pool owners learn this the hard way after a heavy rainstorm or a particularly hot week of evaporation, but once you know what to look for, it becomes second nature.
The skimmer is that plastic rectangle built into the side of your pool wall. Its job is to suck in the top layer of water, catching leaves, bugs, and sunscreen oils before they sink to the bottom. For it to do this job properly, the water needs to be at a specific height. If the water is too low, the skimmer starts sucking in air, which can actually destroy your pool pump. If it's too high, the skimmer can't create the necessary "gulping" action to catch floating debris.
Why the halfway mark is the magic spot
Think of your skimmer like a mouth. If the water is barely touching the bottom lip, it's going to gulp in air along with the water. This leads to air bubbles in your return lines and, eventually, a lost prime in your pump. On the flip side, if the water is over the top of the "mouth," the skimmer can't effectively pull surface debris into the basket. The floating junk will just bob around in the middle of the pool instead of being filtered out.
Most pros recommend keeping the level between one-third and one-half of the way up the skimmer opening. If you have a decorative tile line, this usually translates to the middle of the tiles. Keeping it here gives you a little bit of a "buffer zone." If a few kids jump in and splash some water out, you're still safe. If it rains an inch or two, you're still within the functional range.
What happens when the level drops too low?
We've all had those weeks where the sun is beating down and we forget to top off the pool. When you're asking yourself where should pool water level be because you notice the pump making a weird grinding or sucking noise, you've likely let it get too low.
When the water level falls below the skimmer opening, the pump starts drawing in air. Pools are "closed" hydraulic systems designed to move liquid, not gas. When air enters the system, the pump loses its "prime." This means the motor is spinning at high speeds but isn't actually moving water to cool itself down. If left long enough, the internal seals can melt, the PVC pipes can warp, and you could be looking at a $500 to $1,000 repair bill for a new pump motor.
Low water levels usually happen because of three things: evaporation, heavy use (lots of splashing and cannonballs), or a leak. If you notice you're adding water every single day just to keep it at the halfway mark, you might want to check for a leak behind the light niche or in the liner.
The downsides of a pool that's too full
It's tempting to think that "more is better," especially after a heavy downpour. You might look out at your flooded pool and think it's fine to leave it that way, but a pool that is too full has its own set of problems.
When the water level is near the very top of the skimmer or covering it completely, the skimmer loses its "skimming" ability. For the skimmer to work, there needs to be a bit of a waterfall effect over the weir door (that little flapping gate inside the skimmer). This surface tension break is what pulls in the pollen and floating debris. When the pool is overflowing, the water is stagnant at the top, and all those leaves will eventually get waterlogged and sink to the floor. Now, instead of a simple skimmer basket cleaning, you're out there with a vacuum or a net for an hour.
Additionally, if you have an overflow drain and the water is constantly sitting above it, you're essentially throwing money away in the form of balanced chemicals. Every time it rains and the excess water drains out, your expensive chlorine and stabilizer go right along with it.
Dealing with rain and evaporation
Nature is constantly fighting against your perfect water level. On a hot summer day, it's perfectly normal to lose about a quarter-inch of water to evaporation. If it's windy or the humidity is low, you might lose even more. This is why it's a good habit to check the water level every time you go out to empty the skimmer baskets.
Rain, of course, does the opposite. A big summer thunderstorm can easily raise your water level by two or three inches in an hour. If you wake up and the water is touching the top of the skimmer, it's time to drain some out. Most sand or DE filters have a "waste" or "backwash" setting that makes this easy. If you have a cartridge filter, you might have to use a small submersible pump or open a specific drain valve to bring the level back down to the "sweet spot."
The bucket test: Is it a leak or just the sun?
If you find yourself constantly questioning where should pool water level be because it seems to drop an inch every night, you might have a leak. But before you call a professional leak detection company, try the bucket test. It's a classic DIY trick that saves a lot of money.
- Fill a 5-gallon bucket with pool water and set it on the first or second step of the pool (so the water in the bucket stays at the same temperature as the pool).
- Use a piece of duct tape or a Sharpie to mark the water level inside the bucket.
- Mark the water level of the pool on the outside of the bucket.
- Wait 24 to 48 hours.
If the pool water level drops significantly more than the water inside the bucket, you have a leak. If they both drop about the same amount, it's just evaporation, and you can breathe a sigh of relief.
Adjusting for seasonal changes
Where the water sits also depends on what you're doing with the pool. If you are getting ready to host a massive pool party with ten teenagers, you might actually want to start with the water a little bit lower than the halfway point. Why? Because the "displacement" of ten bodies will raise the water level significantly. If you start at the halfway mark, all that splashing will send gallons of treated water over the deck and down the drains.
Conversely, if you're closing the pool for the winter in a cold climate, you'll usually drain the water well below the skimmer and the return lines. This prevents the water from freezing inside the pipes and cracking them. In that specific scenario, the answer to "where should pool water level be" is usually about 4 to 6 inches below the lowest plumbing line.
Keeping it simple
At the end of the day, don't overthink it. You don't need a ruler or a laser level to get this right. Just walk over to your skimmer, look at the opening, and make sure the water is sitting right around the middle.
If it's a little high after a rain, it's not an emergency, but you'll have a cleaner pool if you drain it back down. If it's a little low, grab the garden hose and top it off while you're out there. Staying on top of this one small task will keep your equipment running smoothly and your water looking clear enough to dive into. After all, the whole point of having a pool is to enjoy it, not to spend your entire weekend troubleshooting pump issues caused by a low water line. Keep it at the halfway mark, and you're good to go.