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A dropping level is usually nothing to worry about
You top up the pool on Saturday. By the following weekend, the water sits a little lower on the tiles. It’s one of the most common things new owners notice, and it often leads to the same worried question. Is something leaking?
Most of the time, the answer is no. Every pool loses some water to the air, day in and day out. It’s a natural process, and on a warm, breezy week it can be more noticeable than you’d expect. Understanding pool evaporation helps you tell normal loss from something that needs a closer look.
In this guide we’ll explain what’s going on, what makes it faster or slower, how to check for a leak, and the simple habits that help you keep more water in your pool. There’s nothing complicated here, and a few small changes can make a real difference.
Why it matters
Losing water isn’t only about topping up. Each time water evaporates, it takes heat with it. Fresh top up water also changes your water balance. So keeping evaporation under control helps your pool stay warmer, clearer and easier to look after.
What pool evaporation actually is
Evaporation happens when water at the surface turns into vapour and drifts off into the air. It happens in any open body of water, from a puddle to a lake. Your pool is no different.
The key thing to understand is that evaporation happens at the surface. The bigger the surface and the more exposed it is, the more water can escape. Depth has very little to do with it. A shallow pool with a large surface can lose more than a deep pool with a small one.
Why the change can look bigger than it is
A drop of a centimetre or two doesn’t sound like much. On the tiles, though, it’s easy to see, and the water level can seem to fall faster than it really is. Across a whole pool surface, even a small drop represents quite a lot of water, which is why regular top ups are normal.
It happens all year
Many people assume evaporation only matters in summer. In fact, it carries on through the year. On cold, dry, windy days, a heated pool can lose a surprising amount, because the gap between the warm water and the cool air is so large. You may even see a mist rising from the surface on a chilly morning.
Only the water leaves
When water evaporates, the minerals and dissolved chemicals stay behind. Over time, this can gradually concentrate things like calcium in the pool. That’s one reason regular testing matters, and why top ups with fresh water are part of normal pool care.
The things that speed up pool evaporation
Several everyday factors affect how fast your pool loses water. Knowing them makes it easier to spot patterns and to decide what to change.
Sun and warmth
Direct sun warms the surface, and warmer water evaporates more readily. A pool in full sun all day will usually lose more than one in partial shade.
Wind
Wind is one of the biggest factors. Moving air carries vapour away from the surface and replaces it with drier air, so evaporation keeps going. Pools on open, exposed sites often notice this most.
Dry air
When the air is humid, it can’t take on as much extra moisture. When it’s dry, it can take on much more. A crisp, dry day can pull water from the pool faster than a muggy one.
Heated water
The warmer your pool compared with the air around it, the faster it will evaporate. In fact, heated pools often see more pool evaporation in the cooler months than in the height of summer, which surprises many owners. This is especially true in spring, autumn and winter, and at night when the air cools down.
Location and layout
Where the pool sits in the garden matters. A pool on a high, open plot will usually lose more than one tucked behind a house or a line of trees. Long, narrow pools set side on to the prevailing wind can catch more of it along their length. None of this means you need to move anything. It simply helps explain why two similar pools in different gardens can behave quite differently.
Splashing and water features
Every splash, dive and cannonball throws water out of the pool. Fountains, waterfalls and jets add to evaporation too, because they break the water into droplets and increase the surface exposed to the air. They look wonderful, but it’s worth running them only when you’re enjoying them.
How to tell evaporation from a leak
If the level seems to be dropping faster than you’d expect, it’s natural to wonder whether there’s a leak. Thankfully, there’s a simple way to get a clearer picture.
The bucket test
This is a widely used check that anyone can do:
- Fill a bucket with pool water to a few centimetres below the rim.
- Stand the bucket on the pool steps so it sits in the water, at a similar temperature.
- Mark the water level inside the bucket and the pool level on the outside of the bucket.
- Leave both for a day or so, with the pump running as normal and no swimming.
- Compare the two drops.
If both have dropped by a similar amount, you’re most likely looking at evaporation. If the pool has dropped noticeably more than the bucket, there may be a leak worth investigating.
Other signs to look out for
A few other clues can point towards a leak rather than normal loss to the air:
- damp patches or soft ground near the pool or equipment
- the level dropping faster when the pump is running
- air bubbles returning through the inlets
- cracks or movement in the surround
If anything like this sounds familiar, it’s worth getting it checked properly. Our guide to pool water loss goes into more detail on what to look for and what to do next.
Simple ways to reduce pool evaporation
The best news is that you have plenty of control here. A few small changes can make a real difference to how often you need to top up.
Use a cover
A cover is by far the most effective tool you have. When the surface is covered, there’s very little space for vapour to escape, and wind can’t reach the water. Covers also help hold in heat and keep leaves and debris out.
There are a few types to choose from:
- Solar bubble covers are light, simple and help trap warmth from the sun. Our guide to solar bubble covers explains how they work.
- Automatic covers glide over the pool at the touch of a button, which makes it easy to cover up every time. Find out more in our guide to automatic pool covers.
Whatever type you choose, the key is to use it. A cover folded up on the side does nothing for your water or your heat.
Shelter from the wind
Hedges, fencing, planting and garden buildings can all help block the wind across your pool. Even a partial windbreak on the most exposed side can help. If you’re still planning your garden, it’s worth thinking about the prevailing wind when deciding where the pool goes.
Be thoughtful with heating
Keeping the water at a comfortable, steady temperature rather than very warm can help reduce loss. Pairing your heating with a cover makes a big difference, because the cover holds in the warmth you’ve paid for.
Run water features wisely
Enjoy your fountains and jets, but switch them off when nobody’s around to see them. The same goes for any feature that sprays or cascades.
Keep splashing in the pool
This one’s easier said than done with children around. Still, gentle swimming, fewer bombs and a well placed step or ledge all help keep more water where it belongs.
Indoor pools lose water too
Pools inside a building or enclosure are more sheltered from wind and sun. Even so, pool evaporation carries on indoors, just in a different way. In an indoor space, that moisture has nowhere to go unless it’s managed.
Humidity and comfort
Warm, moist air can make a pool room feel clammy and can lead to condensation on windows, walls and ceilings. Over time, this can affect finishes and the building itself. That’s why indoor pools usually need a proper ventilation or dehumidification plan, designed with the room in mind.
The cover still helps
Even indoors, a cover is valuable. It reduces how much moisture goes into the room when the pool isn’t in use, and it helps keep the water warm. If you’re planning an indoor pool, talk to us about how the pool, cover and room can work together.
Topping up the right way
Some loss through evaporation is inevitable, so topping up is part of normal pool life. Doing it well keeps things simple.
- Top up little and often rather than waiting for the level to drop a long way.
- Aim for the level your installer recommends, usually around the middle of the skimmer opening.
- Test the water after a top up, as fresh water can change your pH and other readings.
- Keep a note of how often you top up, so you’ll notice if it suddenly changes.
Keeping a simple log
A notebook or a note on your phone is all you need. Jot down the date, roughly how much you topped up and what the weather was doing. After a few weeks you’ll have a clear sense of what’s normal for your pool. If the water level starts dropping faster than your notes suggest it should, you’ll spot it quickly, and you’ll have useful information to share if you do need a professional to take a look.
Your log also helps you see how much difference your cover makes. Many owners are surprised at how much steadier things become once the cover goes on every evening. Tracking pool evaporation this way turns a vague worry into something you can actually see and manage.
If you’re adding chemicals to rebalance, please take care. Follow the label, wear gloves and eye protection, never mix chemicals, always add chemical to water rather than water to chemical, keep swimmers out until the water is balanced and store products away from children and pets.
Water loss questions we get asked a lot
How much water loss is normal?
It varies a lot with weather, shelter, heating and how the pool is used. A steady, gradual drop that matches the conditions is usually normal. A sudden change is worth a closer look.
Should the water level ever drop below the skimmer?
Ideally not. If the level falls too low, the skimmer can draw in air, which isn’t good for the pump. Top up before it gets that far.
Does a cover really help?
Yes. A cover is one of the most effective ways to cut water loss, and it helps with heat and cleanliness too.
Why does my pool lose more water in autumn?
Cooler, drier air and a warm pool create a big temperature gap, which speeds up evaporation. Using a cover every night helps a lot.
Is it safe to top up with tap water?
For most homes, mains water is the simplest way to top up. Just test and rebalance afterwards.
Can I tell if it’s a leak without a professional?
The bucket test is a good first check. If it suggests more than evaporation, it’s best to get a professional to take a look.
Do indoor pools evaporate less?
They’re sheltered from wind and sun, but they still lose water to the air. Managing humidity is an important part of any indoor pool.
Keeping pool evaporation in check all year round
A little water loss is a normal part of owning a pool, and now you know why it happens. Sun, wind, dry air and warm water all play a part, and a good cover is the simplest way to keep more of your water, and its warmth, where it belongs.
If you’d like to talk about covers, heating or a pool that suits your garden, you can explore our full range of pools and see what’s possible. We’re always happy to help you plan a pool that’s easy to enjoy and easy to look after.
Call us on 01483 323 676 or email hello@hilifepools.co.uk for a friendly, no-pressure chat, or get in touch online and we’ll come back to you.
