Pool Safety: Water Parameter Guidelines

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A fun day at the swimming pool or spa can quickly be ruined if the water is not properly maintained.

Pathogenic bacteria, viruses, fungi and protozoa are released by bathers when making contact with water.

Additionally, during swimming activities there is a continuous release of contaminants (urine, saliva, hair, skin, sweat, etc.) into the water.

These contaminants are rich in compounds like ammonia, urea, proteins, fats and amino acids that make pool water an ideal environment for multiplication of the microorganisms and biofilm formation on pool surfaces.

Absent or inadequate chemical (with chlorine or other disinfectants) and physical (flocculation, filtration and back-washing) treatment of pool water can be a serious health risk to the swimmers. [1,2]

For the reasons mentioned above, safety guidelines have been put in place for pools and spas!

Almost every country has hygiene requirements for swimming pools in its legislation that public swimming pools have to follow.

These laws define microbiological, physical and chemical parameters that must be monitored, their permissible range, the method by which they need to be analyzed, how often they need to be analyzed and if the analysis must take place at the swimming pool or spa. [2-5]

From chemical and physical parameters chlorine (free and combined), pH value, ORP or redox potential and temperature have the strictest regulations.

These parameters have a very narrow allowed range and are recommended to be controlled automatically with additional manually performed measurement.

Besides these, there is also the measurement of turbidity, electrical conductivity and many others that affect the hygiene and safety of the pool or spa water. [2-5]

Need assistance?


A wide range of disinfectants can be used for the swimming pool.

The most often used (and also mandatory in public pools) is chlorine that can be introduced in water as sodium hypochlorite (10-15% NaOCl), chorine gas (Cl2), calcium hypochlorite (Ca(OCl)2) or generated by electrolysis. [2]

The added chlorine (in one of the forms above) is found in water as free chlorine (hypochlorous acid, hypochlorite ion or dissolved elemental chlorine) or combined chlorine (chloramines and organic chloramines).

Free chlorine, if in its active form, will attack microorganisms and oxidize contaminants in water.
After the free chlorine reacts, it becomes combined. 

The sum of combined and free chlorine is total chlorine. [2]

Relationship between free, combined and total chlorine

The determination of free and combined chlorine levels can be done using the DPD method as outlined in EN ISO 7393-2.

N,N-dialkyl-1,4-phenylenediamine (DPD) reacts with chlorine to form a magenta colored complex. The intensity of color is indicative of the amount of chlorine in water and can be determined by photometry or visual comparison using a tests kit. 

Because free and combined chorine should be determined at an accuracy of ±0,1 mg/L or better, it is recommended using a photometer.


Pool Line Portable Photometer
for pH, Alkalinity, Free&Total Chlorine and Cyanuric Acid

HI971044 Pool Line Portable Photometer for pH, Alkalinity, Free & Total Chlorine and Cyanuric Acid combines accuracy and ease of use in a simple, portable design.

Free and total chlorine can be determined with ± 0,03 mg/L ± 3 % mg/L of reading accuracy while following the requirements of the ISO 7393-2 standard.

The recommended levels of free and total chlorine depend on what kind of pool is being analyzed [table 1].

Outdoor pools that are subjected also to contamination from the environment and face a constant reduction of chlorine by the sunlight need more chlorine than indoor pools. 

Spas with higher temperatures need more chlorine than cooler pools to keep the bather safe. [2-5]

Country Range Method
0,3 - 0,6 mg/L (free chlorine)

<0,3 (combined chlorine)*
SIST EN ISO 7393-2:1985

(DPD method)
0,2 - 1,0 mg/L (free chlorine)*
HRN EN ISO 7393-2

(DPD method)
0,3 - 1,2 mg/L
if pH value exceeds 7,4 min value is
0,5 mg7L
(free chlorine)

<0,3 (combined chlorine)

(DPD method)

Table 1 – Required free and total chlorine values in public pool in Slovenia, Croatia and Austria

* In cases where in order to ensure conformity of microbiological parameters or when the temperature of the pool is higher than 23; higher values of free chlorine are allowed.


The pH of the pool water needs to be monitored for multiple reasons.

Distribution of HOCl and OCl- in function of pH

The most obvious is that extreme values would cause discomfort to bathers and also damage the equipment, but the allowed range of pH is very narrow (from 6.5 to 7.8 pH, table 2).

The pH value greatly effects the chemistry of the pool water, in particular it dictates what percentage of chlorine is in its active from (HOCl) and the formation of disinfection by-products.

At pH 7,2 about 60% of free chlorine is found as HOCl.

At pH 8,0 only about 20% of active chlorine is active. [2]

The following methods can be used for pH value determination: using litmus paper, the Phenol Red Method (measuring absorbance with a photometer after the addition of Phenol Red or visual comparison using tests kits) or by a pH meter (potentiometric determination).

EN ISO 10523 method specifies that the pH needs to be determined by the most accurate method of the mentioned, that is by using a pH meter with a temperature sensor. 


Waterproof Portable pH / pH-mV / ORP / Temperature

HI991003 Waterproof Portable pH/pH-mV/ORP/Temperature is an ideal choice for professionals at work with the capability to measure three important pool water parameters at once.

It features a portable design, unique titanium body pH/ORP electrode with built-in temperature sensor, Sensor Check™ and simple operating with two buttons. 

For quick checkup at the pool, the Phenol Red method with a photometer (HI971044 pH, Alkalinity, Free&Total Chlorine and Cyanuric Acid Portable Pool Line Photometer – see above at point 1) could also be used. 
The litmus paper method is however not accurate enough.

The recommended levels of pH values depend on what kind of pool is being analyzed [table 2]. 

Country Range Method
6,5 - 7,6 pH

(potentiometric determination)
6,5 - 7,8 pH
HRN EN ISO 10523

(potentiometric determination)
6,5 - 7,8 pH;

6,5 - 7,4 pH for spas
ÖNORM M 6244

(potentiometric determination)

Table 2 – Required pH values in public pool in Slovenia, Croatia and Austria [3-5] 


Almost certainly alkalinity is too low.
The value of total alkalinity should be kept between 75 and 120 ppm CaCO3.

HI971044R Pool Line pH, acidity, chlorine (free and total), cyanuric acid portable photometer is supplied with a carrying case, reagents and HI3890 water hardness test.

Complete kit for understanding crucial chemistry in pool water.


ORP (the oxidation-reduction potential or also redox) indicates the tendency of how oxidizing or reducing the sample is. 

Because disinfection is a process of oxidation, measuring ORP can be used to monitor disinfection efficiency.

For pool water, the ORP value should be above 720 mV (using a silver/silver chloride electrode), but because this value is affected by multiple factors (not just chlorine concentration), 

Appropriate values should be determined on a case-by-case basis [table 3] [2]

Country Range Method
>750 mV
for pH values between 6,5 and 7,3;

>770 mV
for pH values between 7,3 and 7,6*
Redox potential against Ag/AgCl, 3.5 M KCl, result expressed against HSE
>750 mV
for pH values between 6,5 and 7,3;

>770 mV
for pH values between 7,3 and 7,8*
Redox potential against Ag/AgCl, 3.5 M KCl, result expressed against HSE
>700 mV**
Redox potential against Ag/AgCl, 3.5 M KCl

Table 3 – Required ORP values in public pool in Slovenia, Croatia and Austria [3-5] 

* In case of seawater, minimum values are:
>700 mV for pH values between 6,5 and 7,3;
>720 mV for pH values between 7,3 and 7,8

Hanna Instruments offers the perfect solution with HI991003 Waterproof Portable pH/pH-mV/ORP/Temperature (see above at point 2) for simultaneously measuring ORP, pH and temperature.


Values of chlorine, pH, ORP and temperature are in most cases requested to be measured continuously with additional once per day manual measurements.

Hanna Instruments PCA 330 series analyzers continuously monitor, control, and adjust chlorine content and pH value of a sample stream, using the DPD method for measuring chlorine, the HI1005 amplified pH electrode with built-in pt100 temperature sensor and HI2008 platinum ORP electrode.


Although there are no regulations for private pool owners, maintaining hygiene standards should be as important as for public pool owners.

Every pool owner should have equipment for measuring important parameters like chlorine, pH and temperature, but for those who would like to be certain that their pool is safe at any time, automatization is the solution.

Hanna Instruments BL12X Pool Controller Series continuously measure ORP, pH and temperature, while also according to those measurements dose chlorine and acid with built-in peristaltic pumps.

With BL12X private owners can be sure there will always be enough free chlorine in the pool, even in outdoor pools during the strongest sunlight or when a bunch of people jump in the pool during a pool party.


Turbidity is a measurement of the amount of suspended matter in water. 

This parameter is important to control in swimming pools, because it indicates the effectivity of filtration and disinfection.

Also, pool water should be kept clear for the lifeguards to have maximum control. [2]


Pool Line ISO Turbidity Meter

Turbidity is measured according to EN ISO 7027 with a turbidity meter that uses an IR LED light source (860 nm).

HI987134-02 Pool Line ISO turbidity meter meets and also exceeds the requirements of the standard.

HI987134-02 uses the ratio method with two detectors placed at 90° and 180°, that ensures reliable and accurate readings on low turbidity values (that are required for pool water, table 4).

Turbidity values required for pool water [table 4]

Country Range Method
<0,5 NTU
SIST EN ISO 7027:2000
<1 NTU

cloudy/strongly cloudy
Not specified

Table 4: Required turbidity values in public pool in Slovenia, Croatia and Austria [3-5]


Temperature influences proliferation of microorganism, occurrence/speed of chemical reactions and the risk of heart attacks.

Water of convectional swimming pools should have a temperature ranging from 26°C to 30°C in order to be comfortable to.

In hot tubs it is recommended to keep the temperature of water below 40°C. [2]


Pool Line Digital Thermometer

HI985394 Pool Line Digital Thermometer is designed to measure the temperature in swimming pools and hot tubs. 

The weighed AISI 316 stainless steel probe is attached to the meter with a 3 m cable is capable of taking temperature readings at various depths.


Total dissolved solids (TDS)/electrical conductivity (EC) is a water purity indicator. 

The greater concentration of disinfectants, disinfectant-by-products, pollutants originating from bathers or the environment the greater the TDS value.

If TDS/EC is high in comparison to the source water, the pool should be backwashed or diluted. [2]


Pool Line pH/EC Multiparameter Portable Meter

HI981954 Pool Line pH/EC multiparameter portable meter is a waterproof portable logging multiparameter meter that monitors up to 9 different water quality parameters.

It’s multi-sensor probe allows for the measurement of key parameters including electrical conductivity, TDS, pH, ORP and temperature.

The probe transmits readings digitally to the meter, where data points can be displayed and logged.

The complete system is simple to setup and easy to use.


There are also other parameters that are important for ensuring safety and comfort in pool water and also in some cases included in the list of parameters that are required to be measured:

  • Cyanuric acid, ozone, bromine, iodine – other substances that are used during the preparation of pool water.
  • Alkalinity – the measurement of buffering capacity of water.
    Too low values make stabilization of pH impossible.
    Contrary, too high values make controlling pH too difficult.
  • Calcium hardness – the measurement of mineral content in water.
    Too high values cause carbonates to precipitate, making the water cloudy and unpleasant to the skin. 
    Too low values make the water corrosive.
  • Nitrates and phosphates – excess amounts lead to eutrophication.
  • Copper and iron – excess amounts cause staining.


Pool and Spa Multiparameter Photometer

HI83326 multiparameter photometer for pool and spa has pre-programmed methods for 11 key swimming pool parameters – pH (photometrically or potentiometrically), chlorine, cyanuric acid, ozone, bromine, iodine, alkalinity, calcium hardness, nitrate, phosphate, copper and iron.

Have questions?

Contact a Hanna Technical Specialist at info@hannaservice.eu or using our contact form.

  1. Peters, M. (2016), Microbiology in swimming pools: UV-based treatment versus chlorination, Delft University of Technology https://doi.org/10.4233/uuid:6461fab4-564a-4b91-851f-d27c96434991
  2. Bartram, J. (2006), Bartram published Guidelines for Safe Recreational Water Environments Volume 2: Swimming Pools and Similar Environments, Geneva, World Health Organization
  3. http://www.pisrs.si/Pis.web/pregledPredpisa?id=PRAV12491 (from 30.03.2032) 
  4. https://narodne-novine.nn.hr/clanci/sluzbeni/2020_05_59_1186.html (from 30.03.2032)
  5. https://www.ris.bka.gv.at/GeltendeFassung.wxe?Abfrage=Bundesnormen&Gesetzesnummer=20008002 (from 30.03.2032)
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