The Swimming Pool Operators

and Owners Resources Pages

Resource Page 1 - Installation Standards & Recommendations

Items on This Page

  • Pool Turnover Periods
  • Bather Loads
  • Water Chemistry Testing
  • Microbiological Water Testing
  • Water Temperatures
  • Water Heating
  • Sump Grill
  • Skimmers
  • Side Suctions
  • Inlets
  • Level Deck Pools
  • Balance Tanks
  • Pipe Classes
  • Water Velocity in Pipes
  • Filtration
  • Chemical Safety
  • Electrical Safety
  • Gas Safety

There are a number of accepted Standards and Recommendations covering almost every aspect of swimming pool design and consruction. Of course, the Standards and Recommendations for commercial pools are similar to those for the private home pools, but the heavy use that commercial pools endure means that some aspects are different.

The Standards and Recommendations which we discuss here apply to the circulation and filtration design etc., and are the ones we apply to all our Design and Specification work.


Pool TURNOVER Period

This is the theoretical time taken for the total pool volume to pass through the filtration system once.

Example:- Pool Volume = 25,000 gallons. The circulation pump output is 5,000 gallons per hour. 25,000 divided by 5,000 = 5. The Pool Turnover Period is 5 hours, and the Pool Turnover Rate is 5,000 gallons per hour.

(It has been proved that at least 7 complete turnover periods are needed before 99% of the pool water has actually passed through the filters.)

Recommended Pool Turnover Periods

  • Leisure Water Bubble Pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 20 Minutes

  • Teaching Pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 - 1 hour

  • Waterslide Splash Pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 - 1 hour

  • Leisure Waters up to 0.5m deep . . . . . . . . . . . . . . . . . . . . . . . . . . . .Max 0.5 hour

  • Leisure Water 0.5m to 1m deep . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.5 - 1 hour

  • Leisure Waters 1m to 1.5m deep . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 1.5 hours

  • Leisure Pools over 1.5m deep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 2.5 hours

  • Conventional Pools up to 25m long with a 1m shallow end . . . 2.5 - 3 hours

  • Competition Pools 50m long and 2m deep . . . . . . . . . . . . . . . . . . 3 - 4.5 hours

  • Diving Pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 6 hours

  • Residential or Private pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 6 hours

Maximum Bathing Loads

There are two distinct sets of conditions to determine the Maximum Bathing Load. Maximum SAFE bather load, and Maximum DESIGN Bather Load

Maximum SAFE Bathing Load is simply determined from the surface area of the pool, and is the maximum number of bathers who can SAFELY be allowed to use a facility of a given surface area. The depth of water also influences this figure since it has been determined that shallow water can safely support more bathers than deep water. If the SAFE Bather Load is exceeded, it is considered that there will be an unacceptable risk of accidents due to bather collisions, or drownings etc, and that lifeguarding will be impared due to reduced visability to below water level by lifeguards.

The Maximum SAFE Bather load.

  • Shallow Water (under 1m deep) . . . . . 1 bather per 2.2 square metres - (23.7 square feet)

  • Standing Water (1 - 1.5 m deep) . . . . . .1 bather per 2.7 square metres - (29 square feet)

  • Deep Water (over 1.5 m deep) . . . . . . .1 bather per 4 square metres - (43 square feet)

  • Very Deep Water (over 2 m deep) . . . 1 bather per 4 square metres OR Maximum DESIGN Bather load - (whichever is less)

Please Note:- When determining which formula applies to your pool you must take the deepest depth of the pool. Example: A pool has a shallow end depth of 0.8 metres and a deep end depth of 1.8 metres - you must use the formula "Deep Water (over 1.5m deep)" to determine that pool's Safe Bather load.


The Maximum DESIGN Bather load.

The Maximum DESIGN Bathing Load is the number of bathers per Hour that the circulation and filtration equipment can successfully support without losing water quality. This means that the pool water will not begin to get cloudy through excessive dirt and debris, and the Free Chlorine level and pH value will remain within acceptable limits throughout the entire pool.

  • The Maximum DESIGN Bather Load = Pool Circulation Rate (in cubic metres per hour) divided by 1.7

Warning Note:- For example, a teaching pool running 3 x 20 minute sessions per hour with each session comprising of 10 bathers - Just because each session with 10 bathers only lasts 20 minutes this does NOT mean 10 bathers per hour as is sometimes interpreted by swimming teachers attempting to over utilise their pool. It means 30 bathers per hour!


Carrying out MANUAL Testing the pool water is a very important part of the regular "Pool Mainrtenance". It cannot be stressed too strongly that REGULAR, FREQUENT and ACCURATE manual water chemistry tests are essential. The Principle Tests are for pH and Disinfection. Additional tests may be needed for the assesment of residual chemicals. There are further details on Page 9 - Water Tesing and Analysis.

Swimming Pool operators have a legal resposibility to provide a SAFE environment not only for their staff but for the public and any other person who may be on their premises. This responsibility extends to positive knowledge that the swimming pool water chemistry is unlikely to affect the health of any person in or near to the water. This is a Legal "Duty of Care"

Before any pool is opened or made available for use, the Pool Owner or Pool Operator must be satisfied that the water quality is safe for bather use. In the School, Hotel, and Leisure Pool environment this means that the pool water MUST be tested by a competent person using an approved Water Tesing Kit - BEFORE any person is allowed into the pool facility. There must also be some means of positivily confirming that the testing has been carried out - i.e. test results, and a signature in the "OK to Use" column in the pool record book. School pools especially, often suffer from negligence with respect to water testing. Certainly, it is not sufficient for a school swimming instructor to unlock the pool for a class to use because "I wasn't told there was anything wrong" In a case like this the Swimming Instructor could be held liable for negligence because they had not taken "Reasonable Care" to ensure the water was safe.

The pool water chemistry must be regularly tested by a competent person using a suitable Manual Test Kit throughout the time that the pool is available for use. The frequencey of manual testing will depend on (a) whether or not there is any form of automatic or semi-automatic chemical control, (b) the volume of the pool, and (c) the type of use. Typicall,y manual Testing will take place every two or three hours whilst the pool is in use. If the chemical levels are controlled by "hand-dosing" and the pool is busy, testing every hour may be more appropriate.

At the end of the day, the pool should always be tested again before closing up for the night. This will allow any last minute corrections to be achieved so that there will not be a failure of disinfection overnight - during the "recovery period" of the pool. This is important since any overnight failures will usually cause a delay in allowing the pool open for use the next morning.


Since microbiological analysis is usually undertaken away from the pool and it will normally take at least 24 hours before any results are available, the microbiological safety is "Asumptive" - i.e - PROVIDED the pool Disinfection and pH has not failed and has remained constantly above the accepted minimum values, - it can be assumed (short term) that the microbiological quality of the water is satisfactory and safe. This does not however, absolve the Pool Operator of undertaking regular actual microbiological testing. Most commercial pools should have regular microbiological testing at a suitable frequency anywhere between 4 and 26 times per year. Often, a simple Plate Count or TVC will be sufficient, with further investigation and more specific testing if these initial tests show a significant presence of bacteria.


Pool Water Temperature

Recommended Maximum Pool Water Temperatures

  • Competitive swimming & diving, Fitness swimming, Training . . 27 deg C - (80.6 deg F)

  • Recreational, Adult teaching, Conventional main pools . . . . . . . 28 deg C - (82.4 deg F)

  • Childrens teaching, Leisure pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 deg C - (84.2 deg F)

  • Babies, Young children, Disabled & handicapped. . . . . . . . . . . . .30 deg C - (86.0 deg F)

  • The Pool Hall should always be 1 deg C ( 2 deg F) above water temperature at 55% - 65% RH. (Except hot water & Hydrotherapy Pools)

    • Generally, outdoor pools will usually operate at the same or a lower temperature than their indoor equivalents.

    High water temperatures are usually unnecessary and may cause damage or reduce the life span of many items of pool equipment. Liners may lose their elasticity, - pool covers will have a reduced life, - plastic fittings may become brittle and break, - filter underdrains or laterals may become distorted or damaged, - socket unions may loose their shape and leak, - water valves may fail or break, - plastic pipework may become distorted, - excessive evaporation may be lost from the water, - heating costs may be excessively high, - chemical consumption will usually increase, and microbiological activity will increase.

    Concrete Pools

    • The Maximum Heating Rate or Temperature Rise (or fall) for a concrete built pool is 1 deg F per hour ( 1 deg C per 2 hours)
    • Big commercial concrete pools and similar structures will often have a maximum temperature rise (or fall) of 1 deg F per 2 hours ( 1 deg C per 4 hours).

    Exceeding the maximum temperature rise can cause cracks, fractures and leaks in the pool structure due to unequal thermal expansion of the shell etc.

    Probably the worst shock for a pool shell is warm water being drained, and the pool immediately fast filled with cold water. This sort of action can cause terminal and often unrepairable damage to the structure.

    Liner Pools

    Although most liner type pools can enjoy a brisk temperature rise, most manufacturers of vinyl pool liners do not really recommend the water temperature to exceed about 85 deg F (29.4 deg C). If the recommended pool temperatures listed above are followed, this should not be a problem.

    High water temperatures can cause vinyl liners to expand and loose their elastic properties causing wrinkles and creases to appear which are usually impossible to remove. High temperatures can also destroy the oils and polymers in the material, so that the liner rapidly becomes brittle and susceptable to damage. Delamination of the various layers in the vinyl material construction also frequently occurs.

    Some manufactures do produce pool liners which are designed for higher temperatures. However, the manufacturers instructions and conditions must be closely adhered to if damage is to be avoided.

    Direct Heating Gas Heaters

    Direct heating gas and oil heaters should always be installed with a "Delay Off" timer inter-connected between the heater and the circulation pump. This ensures that when the circulation pump is normally "switched off", the heater is automaticaly switched off straight away, but the circulation pump continues running for between 10 and 30 minutes (depending on the size of heater). This ensures that the circulation pump is not stopped while the heater is still hot.

    Considerable damage can be caused to Direct Gas Heaters if the circulation water suddenly stops, particularly if the heater was actually fired up and running at the time of the pump being stopped.

    It is essential that all Direct Gas Heaters are switched off for at least 10 - 30 minutes (depending on heater size) before the the circulation pump is stopped


    Number of Sump Grills.

    There must always be a minimum of 2 sump drains, at least 2 metres apart, in every pool. All sump drains must be directly connected to each other so that there can never be the possibility of only one suction point in operation. In practise this means that all the sum drains are interconnected in the base of the pool to one sump suction pipe which is routed to the plantroom. There have been too many accidents where swimmers (both adults and children) have been seriously injured or drowned through being caught against a single sump grill.

    Maximum Proportion of Water Through the Sump.

    • Normal leisure and home pools - 30%
    • Teaching and Childrens Pools - 20%
    • Hydrotherapy and other hot pools - 10%

    The surface of the pool water is usually the most polluted part, with body oils and grease, sweat, skin debris and other pollutants usually within the top 6 inches. It is therefore essential that there is good surface skimming by either enough Skimmer units built into the pool shell, or by Level Deck surface skimming so that at least 70% of the pool water is drawn from the pool surface for filtration and treatment.

    Velocity of Water Through the Sump Grills.

    • Water less than 1 metre deep - Max velocity 1/2 ft per second
    • Water 1 - 1.5 metres deep - Max velocity 1ft per second
    • Water greater than 1.5 metres deep - Max velocity 1.5 ft per second

    It is an essential safety aspect that the water velocity through the sump grills is never likely to cause danger to any pool users.

    The number of sumps required must be calculated on the basis of 100% sump suction, since there may be times when the pool is in use with the surface draw-off not operating. It is essential that these figures are calculated, and not simply guessed.


    The recommended ideal flowrate through a conventional skimmer is usually about 5 cubic metres per hour - about 1,100 imperial gallons per hour. The absolute maximum acceptable flowrate is around 7.5 cubic metres per hour - about 1650 imperial gallons per hour - based on standard swimming pool skimmers - NOT the small spa skimmers.

    Since most of the pollutants are found at the water surface of the pool or spa. it is essential that there is a high percantage of surface skimming, especially on warmer pools where there is more body oil and grease lost to the water..

    The correct installation of a skimmer for a commercial pool is shown below. The Balance Pipe ensure that water will still flow into the skimmer suction if the level has dropped below the skimmer mouth, - after backwashing, for instance, and this avoids the dangerous use of 100% suction through the sump drains.

    Water enters the Balance Pipe via an adjustable inlet fitting, and this is adjusted to provide just enough water to keep the suction flooded when the water depth is at the lowest expected level after a good filter backwash. Once the water level is raised to the skimmer mouth, almost all the water takes the line of least resistance and flows into the skimmer via the skimmer mouth.

    It is essential that ALL the skimmers at a pool are installed the same way. Intalling only a few Skimmers with Balance Pipes will still result in the suction pulling air from the other skimmers - and a loss of prime to the pump.

    Please wait while the drawing of a skimmer installation is loaded.

    Balance Pipes can be omitted on lightly used residential pools in some circumstances. For instance, pool installers or often reluctant to have any more skin fitting on a domestic liner pool than is absolutely necessary, because each perforation of the liner is a potential for leaks.

    By definition, Skimmers are constantly drawing the surface water where all the body oils and grease is present, and it is essential that regular waterline cleaning includes the scum line inside the skimmer body as well as the pool shell scumline.


    Side Suction Fittings

    The usage of side suction fittings, especially when attempting to "upgrade the circulation" of a swimming pool is extremely dangerous and should be avoided at all costs. Water velocities at side suctions are frequently exccesively high and the position of them makes hair entrapment very likely.

    In order to "Upgrade" the circulation of a swimming pool it is far safer and far more useful to install extra skimmers.

    Inlet Water Velocity

    Section Under Construction and will be uploaded soon

    Level Deck Overflow Channels

    The Level Deck Drainage Channels should be capable of holding 125% of the Surge Dispalcement volume

    The drainage pipes from the overflow channel to the Balance Tank should be capapble of delivering 125% of the maximum total pool turnover rate into the Balance Tank.


    Level Deck Balance Tanks

    The Level Deck Pool Balance Tank should be capable of taking the Total Displacement of the Maximum Design Bather Load or the Maximum Safe Bather Load - whichever is the greater. There should also be a provision for surge values (splashover), and this volume will be determined by the type of pool and use it will receive when busy.

    It is important to remember that EVERY pool will generate a "Scum Line" of body grease and dirt at the waterline. In the case of a Level Deck pool, this Scum Line will be concentrated on the Balance Tank walls, and must be frequently and regularly removed and cleaned.

    Balance Tanks are an extension of the pool itself, and must be treated as such -

    • The Tank Shell Finish should be smooth to facilitate easy cleaning - ideally finished with large white tiles.
    • Access to the inside of the Balance Tank should be easy and quick - to encourage regular inspections and cleaning.
    • The Balance tank should be able to be easily drained, and have sufficient headroom inside to allow regular inspection and cleaning.
    • For safety reasons there should never be more than 3m of ceiling space without an access point in the Balance Tank - i.e. an operative inside the balance tank is never more than 1.5m from an access hatchway.

    Automatic Water Top-Up

    The Automatic Top-Up unit installed at the side of the pool usually consists of a recess connected to the pool water via a 1.5" pipe - so the water level inside the unit is the same as that in the pool. A float valve arrangement controls the flow of water into the unit to top-up the pool water.

    It is essential that the Mains Water Supply is not connected directly to the Auto Top-Up unit.

    Serious contamination of the mains water could occur if the mains supply pressure was to drop for any reason, and pool water was drawn into the supply pipe.

    A suitable "Break-Tank" should always be installed at a convienient location (usually the Plant Room). Here, the water level in the Break Tank is controlled by a float valve connected to the incoming mains water supply. The water in the break tank is gravity fed to the float valve in the automatic top-up unit adjacent to the pool.


    Pipe Materials and Class (wall thickness)

    The pipework used for swimming pools circulation systems is normally classified by its wall thickness and wall strength. The wall thickness varies according to the pipe diameter. It must be remembered that the controlled size is the external diameter, since this has to accurately fit inside a wide range of pipe connections. Most plastic pipework for swimming pool use is either PVC or ABS. The most common class used (particularly for domestic pools) is Class C.

    Class D pipe has a slightly thicker wall than Class C, and Class E is even thicker. Class T is the thickest walled pipe, and the wall is thick enough for threads to be cut directly into the plastic.

    ABS pipe tends to resist shattering a little more than PVC, so ABS Class D or Class E pipe is often specified where the pipework is to be buried below ground, or under flooring etc.

    Water Velocity in Pipework

    The velocity of water within a pipe is subjected to physical resistance due to friction and turbulance. This can easily be demonstrated with a long garden hosepipe. Although the water may gush rapidly out of the tap or standpipe, by the time it comes out of the hose at the other end the velocity will have significantly slowed. The same occurs in swimming pool pipework, and all pipe installations must have the pipe sizes calculated in order for the water volume delivered through the pipe is not too high for the pipe diameter.

    • The maximum velocity in any suction pipe must not exceed 5 feet per second (1.52 metres per second).

    • The maximum velocity in any pressure pipe must not exceed 9 feet per second (2.74 metres per second).

    On large commercial installations, the circulation pumps will frequently have much smaller pipe flange couplings than the pipe work connecting to them. On these installations, conical pipe adaptors are often fitted each side of the pump to allow a smooth transition from the very high velocity found within the pump to the relatively slow velocity required within the pipework.



    Filtration Rate

    The Filtration Rate is the speed or velocity of the water through the filtration media. The slower the Filtration Rate - the more effective the filtration.

    • Big or heavily used commercial pools will normaly use LOW filtration Rates.

    • Schools, hotels, other commercial pools, and heavily used private pools will usually have a MEDIUM fitration rate.

    • HIGH rate filtration is usually only suitable for private home pools,

    The Filtration Rate is measured in Cubic metres of water per Square metre of Filter Surface Area per Hour - ( CuMtrs/SqrMtr/Hr or m3/m2/hr )

    OR Gallons per Square Foot of Filter Surface Area per Hour- ( Gall/SqFt/Hr or gal/ft2/hr

    Filtration Rates for Sand Filters (Metric rates)

    • LOW RATE FILTRATION - Less than 10 m3/m2/hr

    • MEDIUM RATE FILTRATION -11 m3/m2/hr to 30 m3m2/hr

    • HIGH RATE FILTRATION - 31 m3/m2/hr to 50 m3/m2/hr

    (NOTE : - Many Sand Filters have a maximum Filtration Rate of 45 m3/m2/hr)

    Filtration Rates for Sand Filters (Imperial Rates)

    • LOW RATE FILTRATION - 200 gal/ft2/hr or less

    • MEDIUM RATE FILTRATION - Above 200 gal/ft2/hr to 600 ga/ft2/hr

    • HIGH RATE FILTRATION - Above 600 gal/ft2/hr to 1000 gal/ft2/hr

    Please note:- It is important that the maximum filtration rate determined by the filter manufacturer is not exceed. Excessively high filtration rates will cause debris to be "stripped through" the filtration media, and distortion and damage to the filter underdrains. Too many Pool Installers still do not calculate filtration velocities and simply guess. They are not helped by unscrupulous equipment distributors who offer mismatched pump and filter kits in their catalogs. It cannot be too strongly emphasised that correctly designing an efficient and effective swimming pool circulation & filtration system involves performing a lot of calculations.


    Backwashing the Filters

    There are THREE criteria for prompting filter backwashing :-

    1. Each filter must be backwashed at least ONCE per WEEK

    2. Each filter must be backwashed when the pressure gauges indicate a pressure RISE of around 3 lbs sq inch.

    3. Filter backwashing will be prompted in order that sufficient topping up with fresh water follows so that one or more residual chemicals are controlled by dilution. (NB - Residual control could be achieved by simply dumping water, however it is a more efficient use of resources to use the water to clean the filters while discardeding it.)

    • In the absence of residual testing, all commercially operated pools should dump at least 10% of the pool volume per week.

    • European recommendations are that 30 litres of pool water per bather per day is replaced with fresh.

    Please note:- A number of distribuors and manufacturers make claims that their "equipment of product reduces the need to backwash" ! It must be remembered that cleaning the filters is only part of the Backwash function. Replacement of water in a swimming pool is essential for controlling undesirable residual chemicals which will otherwise build up in the water. Claims by manufacturers of "add-on" equipment that in some instance, they claim reduces the nead to backwash by up to 80% do NOT take into account residual and trace chemicals which can ONLY be controlled by dilution. Likewise, one equipment distributor has suggested that in order to save water the backwash effluant is passed through a cartridge filter "supplied by them", of course and then this filtered water is returned back to the pool. Although this was suggested for residential pools, there was no thought on how the various chemical residuals remaining in the water would be controlled.

    Any reduction in poolwater replacement MUST be accompanied by careful monitoring of all the residuals to ensure that dangerously high levels are not allowed to develop.

    Filter Media

    The filter media in a normal leisure pool sand filter should be checked at least once per year. This is achieved by opening the filter and examining the media. Any signs of contamination should prompt a media change.

    Hot water pools such as Teaching Pools, Hydrotherapy Pools, and Spas should have the filter media checked about every 3 months.

    Electrical Safety

    In the UK the electrical installation rules and regulations are provided by the Institution of Electrical Engineers. These regulations are enforcable, and failure to observe them could result in severe penalties. The current rules are all published in the IEE Regulations. We consider it is essential that any person contemplating carrying out any electrical repairs or installations within the UK, has a copy of this publication to ensure that all the electrical activities are carried out to an approved manner and standard.

    One of the most important recent regulations is the creation of the "Zone" system of regulations. Three Zones are created, - Zone A is within the pool shell, - Zone B is an area extending 2 metres from the edge of the pool and a height of 2.5 metres above the highest part of the pool, - Zone C is an extension of Zone B for a further 1.5 metres.

    In essence, no electrical equipment is allowed inside Zone A or Zone B unless it is "SELV" (Safe Electrical Low Voltage) of not more than 12 volts (i.e. - underwater lights)

    Another regulation often ignored is the provision of equipotential bonding on all electrically conductive equipment. This implies that all ladders and handrails etc. must be electrically joined and earthed to all other all other metalic equipment in the vicinity.

    We understand that if a recent regulation creates a situation where an older installation of electrical equipment would now be illegal, - unless that installation is believed dangerous the owner would not be forced to carry out remedial work to conform to the current regulations. However, any repairs or replacements to that equipment would be illegal and the engineer would be just as liable as if he had carried out the illegal installion in full after the regulation came into force.

    Gas Safety

    In the UK, by Law, all businesses installing or servicing gas appliances MUST be registered with GAS SAFE. Any person working on a gas appliance must be recognised and approved by GAS SAFE. There are heavy fines for persons not registered with GAS SAFE and found working on gas appliances.

    One of the most important aspects of gas heater installation is the provision of sufficient air to enable the combustion to take place correctly. If the gas heater is not supplied with enough air, - Carbon Monoxide will be produced in large quantities, and this odourless gas quickly KILLS.

    Even a relatively small swimming pool gas heater can require quite large wall ventilator openings, correctly positioned.

    Gas heaters should be serviced every year (ideally in the spring) by a Qualified and Registered GAS SAFE Engineer who is fully familiar with swimming pool gas heaters.


    Section Under Construction and will be uploaded soon


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