Pool Skimmer Sizing: How Many, How Much Flow, or Overflow

Sauna Dekor Spa Solutions engineering team, Istanbul · project and press enquiries: Alican Aykaç, Managing Partner

Updated: 12 November 2026

Above those limits, or where many swimmers use the pool at once, the surface is skimmed by a perimeter overflow gutter instead. In this guide, Sauna Dekor Spa Solutions gives the rules, a worked count for four pool sizes, and the point at which a hotel, residential or villa pool should move from skimmers to overflow. The figures come from the US Model Aquatic Health Code and the World Health Organization, both listed at the end; the local authority on each project has the final word.

Table of contents

• What does a pool skimmer do?
• How many skimmers does a pool need?
• How much water should each skimmer take?
• How many skimmers for common pool sizes?
• Where should the skimmers go?
• When does a pool need overflow instead of skimmers?
• What does an overflow system need that a skimmer pool does not?
• How level must the skimmers and the water line be?
• Which suits a villa, a residents’ pool and a hotel pool?
• Which pools have we built?
• Frequently asked questions

It removes the dirtiest water first. Floating debris, sunscreen, skin oils and dust collect in the top few millimetres, and the World Health Organization recommends taking 75 to 80 % of the circulated water from the surface, with the rest from the bottom. A pool skimmer is one of the two ways of doing that; the other is an overflow gutter.

A skimmer is a box built into the pool wall with an opening at the water line. Water flows over a floating hinged weir, which stops debris being washed back out when the pump stops or waves hit the wall, into a removable basket that catches leaves and insects, and on to the pump and filter. Wide-angle skimmers have openings of up to about 600 mm.

The skimmer only works while the water line sits inside its opening. That single fact explains most of the rules below: how many skimmers, how level they must be, how much flow each needs, and why large or busy pools use a gutter instead. The wider picture of pool circulation, from inlets to filter, is covered in our note on better water circulation in a pool.

At least one pool skimmer for every 46 m² of water surface, or fraction of it, under section 4.7.1.5.1.2 of the 2024 Model Aquatic Health Code. A pool of 8 × 4 m (32 m²) needs one; 12 × 6 m (72 m²) needs two; 15 × 7 m (105 m²) needs three; 20 × 8 m (160 m²) needs four.

That is a minimum, not a target. The same section says additional skimmers may be needed for effective skimming on site, and names outdoor pools affected by wind and pools with heavy contaminant loading as the cases. An outdoor pool in Dubai, Doha or Riyadh that collects wind-blown dust most afternoons belongs in that second group, and one extra skimmer on the downwind side is usually cheaper than a daily manual clean.

The code also limits the shape: pools using skimmers shall not exceed 9.1 m in width (section 4.7.1.5.1.5). A skimmer draws from a short length of wall, and across a wider pool the far side is too far away for its pull to reach the surface reliably.

The skimmer and overflow edges we build on a cast shell are shown on our shotcrete swimming pool page.

About 114 L/min, or 14 L/min per 2.5 cm of weir width, whichever is greater, according to the Annex of the 2024 Model Aquatic Health Code. Each skimmer must also stay within the maximum on its own data plate, and the skimmers together must be able to carry up to 100 % of the pool’s design recirculation flow.

The flow check works in both directions. Too little flow and the weir barely moves, so the skimmer stops pulling the surface. Too much, and it draws water from below the surface rather than the surface itself, and can pull air into the pump. More skimmers are therefore not automatically better: spread a small flow across too many and none of them skims well.

The flow comes from the turnover. The code’s maximum turnover for general pools is 6 hours; UK practice quoted by the WHO uses 2.5 to 3 hours for conventional pools up to 25 m long. For a 12 × 6 m pool at an average 1.4 m depth, 100.8 m³ turned over in 4 hours is 25.2 m³/h; 80 % from the surface is 20.2 m³/h, or 168 L/min across 2 skimmers, comfortably above 114 L/min each.

Between one and four for pools from 32 m² to 160 m², with each skimmer carrying 149 to 187 L/min in the worked examples below. Above about 149 m², the Code’s Annex notes that skimmer use could be limited in favour of a perimeter gutter, which is why the largest row is a borderline case.

On the side the surface water naturally moves towards, at least 1.5 m from any inlet. The code asks for skimmers located to skim the entire water surface, clear of steps and small recesses where flow is restricted, with wind direction considered in their number and placement, and it places inlets at least 1.5 m from a skimmer (section 4.7.1.3.3.3.2).

In practice the inlets on one side push the surface towards the skimmers on the other. Outdoors, the prevailing wind on the site does the same job for free if the skimmers sit on the downwind wall, and works against them if they sit upwind. On a roof pool, where wind comes round the building’s edges, it is worth watching the site for a few afternoons before the layout is fixed.

Steps, benches and corners are the places debris collects. The code keeps skimmers out of recesses so that their pull is not throttled, and adds inlets at each stairway and recessed area to keep water moving there. The same logic appears in routine care, which our guide on how to maintain a pool walks through from the operator’s side.

When it is wider than 9.1 m, larger than about 149 m², or used by many swimmers at once. The Code’s Annex gives the reason with an example: a 9.1 × 15.2 m pool served by three 30 cm skimmers draws all its skimmed water from 0.9 m of wall, just 1.9 % of the perimeter, leaving the rest to form scum lines and dead corners.

An overflow pool solves that by letting the water run over the whole edge into a channel, so every metre of perimeter skims. The Annex notes that practical experience favours gutters for having no scum lines and no stagnant corners, and that heavily used pools can hit hydraulic limits with in-pool surge that a separate balance tank avoids.

There is also a design reason. With overflow the water sits level with the deck, which Sport England’s pool guidance prefers for easy access in and out of the water, and which most hotel and residential towers want for the look of the pool hall. A skimmer pool always has a visible band of wall between the water and the coping.

A balance tank, a larger channel and tighter tolerances. The code asks for a gutter that removes at least 125 % of the design recirculation flow, a net surge capacity of 40.7 litres per m² of pool surface, automatic make-up water, and a gutter level to within ±1.6 mm around the whole perimeter.

The balance tank holds the water displaced by swimmers so that it is not lost to the drain. For a 25 × 12.5 m pool of 312.5 m², the minimum net surge volume is 312.5 × 40.7 = 12,719 litres, about 12.7 m³, before any allowance for backwashing. That tank, its pipework and its access have to be found in the structure below the pool hall, which is why the choice between skimmers and overflow is made at concept stage.

Overflow comes in several forms, and our own pool work uses four: standard overflow, elevated overflow, perimeter overflow for private pools only, and Wiesbaden overflow with its ceramic channel. Hot, dry air in the Gulf also means more evaporation, and in an overflow pool the automatic make-up that replaces it keeps the water at the gutter lip, which is what keeps it skimming.

Within ±6.4 mm between skimmers, and within ±1.6 mm along a gutter. The code also asks for each skimmer weir to adjust automatically over at least 10.2 cm of water level, and for a waterline finish of 152 to 305 mm in skimmer pools against at least 51 mm in gutter pools.

Those tolerances are the builder’s side of the rule. A skimmer set 10 mm higher than its neighbour runs dry while the other takes all the flow; a gutter out of level overflows on one side and stays dry on the other. Both are decided when the shell is cast and the copings are laid, and neither can be fixed with a pump setting afterwards.

One fitting is now out: the code prohibits skimmer equalizer lines on new construction and substantial alterations, because a suction line in the pool wall without a certified cover is an entrapment risk. Existing pools that still have them are fitted with compliant covers.

Skimmers for most villa pools up to about 50 m², either system for residents’ pools up to 9.1 m wide, and overflow for hotel pools, lap pools of 25 m and anything wider than 9.1 m. The choice follows surface area, width, the number of swimmers and the look of the pool hall.

A villa pool of 8 × 4 m in a garden in Abu Dhabi works well with one or two skimmers, placed downwind. A residents’ pool of 12 × 6 m on a tower podium can use two skimmers, but many developers choose overflow for the level water line. A 25 m hotel or school pool with 5 lanes of 2.0 m is 10 m wide, beyond 9.1 m, and needs a gutter and balance tank.

Indoor and outdoor pools differ mainly in the load on the surface. Our pages on the indoor swimming pool and the outdoor swimming pool cover the hall climate and the plant for each, and our Abu Dhabi page and our guide for choosing a pool contractor in Dubai cover projects in the UAE.

Pools on our reference list include the Heybeliada Olympic swimming pool in Istanbul, hotel pools for Four Seasons in Baku and Hyatt Regency in İzmir, the indoor pool at Tahincioğlu Nidapark in Istanbul and pools for 8 İstek Foundation school campuses, as well as private villa pools in Bodrum and Istanbul. More of our delivered work is on the projects page.

We build turnkey pools: shell, waterproofing, equipment package, installation and commissioning. The choice between skimmers and overflow is made on each of those projects from the same four questions this guide asks: surface area, width, the number of swimmers and the level of the water line the architect wants.

Sauna Dekor has designed and built saunas, steam rooms, hammams and pools since 1987: 40 years of manufacturing in Istanbul, in our own facility in İkitelli OSB, with a team of 19 employees, working under TS EN ISO 9001:2015, and with 5,000+ projects in 41+ countries.

We do not manufacture skimmers, pumps, filters or heat pumps; their manufacturers make them, and any certification of that equipment belongs to them. The TS EN ISO 9001:2015 certificate is ours. On the work we deliver, the terms are a 24-month warranty on workmanship and manufacturing; 24-month manufacturer’s warranty on electrical and mechanical equipment; 5-year warranty on structure and waterproofing.

Skimmers, filters and pumps are checked on every visit of our pool maintenance service.