How Much Does a Swimming Pool Cost to Fill and Maintain?

The phone call that starts every pool season

A client rang me last spring in a mild panic. He had just had a 10-metre by 5-metre inground pool installed — nice rectangular job, 1.2 metres at the shallow end, 2.4 at the deep end. The build had come in on budget. The landscaping around it looked great. Then he turned on the garden hose and asked me how long it would take to fill. When I told him he was looking at roughly 60,000 litres of water and gave him a ballpark on what that would cost, there was a long silence on the other end of the line.

That silence is more common than you would think. People budget carefully for the pool itself — the excavation, the shell, the coping and tiling — and then treat the running costs as an afterthought. But a swimming pool is not a one-off purchase. It is an ongoing system that consumes water, electricity, and chemicals every single week of the year, whether you are swimming in it or not. The pump does not care that it is January.

This guide walks you through the three big running costs — water volume, water usage over time, and electricity — so you can put real numbers on what your pool actually costs to operate. No guessing, no nasty surprises on the utility bill.

How much water does your pool actually hold?

Everything starts with knowing how much water your pool holds. You need this number to calculate fill costs, chemical dosing, heating requirements, and pump sizing. Get it wrong and every downstream number is off.

Pool volume depends on shape and depth. A simple rectangular pool is length times width times average depth. But most pools are not a uniform depth — they have a shallow end, a deep end, and a slope or step between them. The average depth is what matters: add the shallow depth to the deep depth and divide by two. For our client’s pool that was (1.2 + 2.4) / 2 = 1.8 metres average depth, giving 10 x 5 x 1.8 = 90 cubic metres, which is roughly 90,000 litres.

Round and oval pools use a different formula, and kidney-shaped or freeform pools are trickier still — you usually need to break them into simpler sections and add the volumes together.

Use the Pool Volume Calculator to get an accurate figure for your specific pool shape and dimensions:

Write that number down. You will use it repeatedly — for initial fill cost, for calculating top-up water through the season, and for working out chemical quantities. It is the single most important number in pool ownership.

It also helps you separate the drama from the maths. A pool can feel enormous when you’re standing beside it with a hose, but once you know the actual litres or gallons, the rest of the decisions become much more practical. You can price the initial fill, estimate chemical dosing more accurately, and compare equipment choices without hand-waving.

What does it cost to fill a pool and keep topping it up?

Here is something that catches new pool owners off guard: you do not just fill the pool once and forget about it. Evaporation, splash-out, backwashing the filter, and the occasional leak mean you are constantly replacing water. In a warm climate, a typical uncovered pool can lose 25 to 50 millimetres of water per week to evaporation alone. Over a five-month summer, that adds up to a significant volume.

For our 10x5 metre pool, losing 30mm per week across 20 weeks means about 30,000 litres of replacement water over the season — roughly a third of the pool’s total volume. If you are on metered water, that is a cost you need to budget for. And that is before you account for backwashing, which flushes a few hundred litres down the drain every time you clean the filter.

The Water Usage Calculator helps you estimate ongoing water consumption based on your usage patterns:

A pool cover is the single most effective thing you can do to reduce water loss. A decent solar cover cuts evaporation by 90 percent or more and also reduces heat loss overnight, which saves on heating costs. I tell every pool owner the same thing: if you are only going to buy one accessory, make it a cover. It pays for itself within the first season.

One UK-specific wrinkle is whether you are on a water meter and how your water company handles wastewater charges. Some owners focus only on the incoming water rate and forget that sewerage charges may sit on the same bill structure. Others are on unmetered arrangements and feel the top-up cost differently. The calculator gives you the volume side of the equation; your local tariff tells you what that volume actually means in money.

Is it normal evaporation or do you have a leak?

This is the question that usually arrives about three weeks after the first exciting pool fill. A bit of water loss is normal. Warm weather, wind, low humidity, splashing, backwashing and vacuum-to-waste all move water out of the pool. But once owners start topping up more often than they expected, every litre feels suspicious.

The simplest check is the bucket test. Fill a bucket with pool water, set it on a pool step so the water inside the bucket sits at roughly the same level as the pool water outside it, then mark both water lines. Leave the pump running in its usual pattern for 24 hours. If the pool level drops noticeably more than the bucket level, you are probably losing water somewhere other than normal evaporation. If both levels fall by about the same amount, evaporation is the more likely culprit.

That matters because the budget response is different. If it is evaporation, the fix is usually a cover, less aggressive backwashing, and being realistic about how much heated open water costs in a breezy UK spring. If it is a leak, continuing to “just top it up” can turn a manageable repair into a lining, pipework or ground-movement problem. The calculators on this page help you price normal ownership. They are also useful for spotting when your real water use has drifted beyond what normal ownership should look like.

How much electricity does a pool really use?

Water is the visible expense. Electricity is the invisible one, and it is usually larger. A residential pool has several electrical loads running simultaneously, and they add up fast.

The pump is the biggest draw. A standard single-speed pool pump runs at about 1,100 to 1,500 watts. Best practice says you should turn over the entire pool volume at least once every eight to twelve hours, which means most pumps run six to ten hours a day. At 1,500 watts for eight hours, that is 12 kWh per day — every day, all season. Over a six-month period, the pump alone can consume over 2,000 kWh.

The heater is next if you have one. An electric heat pump for a pool typically draws 3,000 to 5,000 watts. Gas heaters use a different fuel source, but electric ones hit the electricity bill hard. Even running a heat pump for four hours a day adds 12 to 20 kWh daily.

The chlorinator, if you have a salt system, adds another 500 to 700 watts while it is running. Robotic pool cleaners draw 150 to 300 watts per cleaning cycle. Pool lights, automation controllers, and water features all contribute smaller but persistent loads.

Use the Electricity Cost Calculator to price out each of these loads individually. Plug in the wattage, the hours per day, and your electricity rate, and you will see exactly what each piece of equipment costs to run:

The rookie mistake here is assuming the pump only needs to run a few hours a day. Under-running the pump means poor water circulation, which means algae, which means shock-dosing with chemicals, which costs more than the electricity you saved. Run the pump long enough to turn the water over properly. If the electricity cost looks painful, the answer is not to run it less — it is to switch to a variable-speed pump, which can cut pump energy consumption by 60 to 70 percent compared to a single-speed unit.

This is where it helps to price each load separately instead of lumping everything under “the pool”. A pump that runs every day is a different problem from a heater you only use on weekends, and both are different again from lights or a robotic cleaner. Once you can see the annual cost of each piece of kit, it becomes much easier to decide whether the smarter upgrade is a cover, a pump replacement, a timer change, or simply lowering the target water temperature.

The hidden costs people forget

Beyond water and electricity, there is a steady drip of other expenses that add up over a full year:

• Chemicals. Chlorine, pH adjusters, algaecide, stabiliser, and shock treatments. Budget roughly 50 to 100 per month during swimming season depending on your pool size and local water chemistry.
• Filter media. Sand filters need new sand every five to seven years. Cartridge filters need replacement cartridges annually. DE (diatomaceous earth) filters need fresh DE after every backwash.
• Winterising and opening. If you are in a climate that freezes, you need to blow out the plumbing lines, add antifreeze, and fit a winter cover each autumn, then reverse the process in spring. Many people hire a service for this, and it typically runs a few hundred per visit.
• Repairs. Pump seals wear out. Heater elements fail. Liners develop leaks. Automation boards corrode. A pool has a lot of moving parts, and something will need attention every couple of years. Set aside a small annual maintenance fund rather than being caught out by a pump failure in July.

Heating also deserves its own mental category because it can completely change the economics. A pool that is filtered and chlorinated but not heated is one thing. A pool that is held at a very comfortable temperature from spring through autumn is another. The fill cost might be a one-off surprise, but the heater is where many owners quietly move from “manageable luxury” to “why is the meter spinning again?”

Putting it all together

Here is a rough annual breakdown for a typical medium-sized pool (40,000 to 60,000 litres) in a temperate climate with a six-month swimming season:

• Water (fill and top-up): varies by local rates, but typically a meaningful line item on metered supply
• Electricity (pump, heater, chlorinator): often the single largest ongoing cost, particularly with electric heating
• Chemicals: a consistent monthly expense that scales with pool volume
• Maintenance and repairs: variable, but plan for it rather than hoping nothing breaks

The total varies enormously by region, pool size, equipment choices, and how warm you like the water. That is exactly why running the numbers with the calculators above matters — generic estimates from the internet are useless when your pool, your climate, and your electricity rate are all specific to you.

How do you cut pool running costs without creating new problems?

If the numbers look steep, there are practical ways to bring them down without sacrificing water quality:

Invest in a variable-speed pump. This is the single biggest lever you have. Variable-speed pumps adjust their motor speed to match the demand, running slowly during normal filtration and ramping up only for tasks that need higher flow. The energy savings are substantial and the payback period is typically two to three years.

Use a pool cover religiously. Covers reduce evaporation, heat loss, and debris entry. Less debris means less filter backwashing, which means less water replacement. It is a virtuous cycle.

Optimise your pump schedule. Run the pump during off-peak electricity hours if your tariff has time-of-use pricing. The water does not care what time it gets filtered.

Right-size your equipment. An oversized pump wastes energy. An oversized heater cycles inefficiently. Match your equipment to your actual pool volume — which, again, is why calculating that volume accurately at the start is so important.

A pool is a genuine luxury, and it costs real money to keep running. But there is a big difference between spending blindly and spending with your eyes open. Know your numbers, plan your budget, and you will enjoy the pool without dreading the utility bills.