Bathing water can contain various microorganisms that are harmless to humans. If the total number of these microorganisms exceeds a certain concentration in the bathing water, this indicates inadequate operation of the treatment system – associated with an increased risk for the bather. If the upper value of DIN 19643 for the general bacterial count of 100 CFU/ml is exceeded, the following measures are recommended (source: Federal Environment Agency):

• Checking measured values of auxiliary hygiene parameters such as free chlorine, pH value and redox voltage

• Calibration of the measuring and control system

• Corrections in the event of setpoint deviations on the measuring and control system, for example by increasing the quantity of certain additives added. This can mean increasing the concentration of free chlorine and/or correcting the pH value in the pool

• Checking and regulating the visitor frequency and addition of fresh water, carrying out a filter rinse
• Arrange for follow-up samples

E. coli (Escherichia coli) is a natural human intestinal germ that can enter the pool water through excretions or excretion residues. These excretions are often not visible to the naked eye. If contaminated bath water is swallowed, dangerous diarrheal diseases can occur. Although E. coli itself can only cause infections in rare cases, its presence indicates that pathogens from the intestine, such as noroviruses or salmonella, may have entered the water in addition to E. coli. If the upper DIN 19643 value for E. coli of 0 CFU/100 ml is exceeded, the following measures are recommended (source: Federal Environment Agency):

• Immediate filter flushing

• High chlorination of the pool water after the end of operation (documentation sheet for high chlorination)

• Filter disinfection (with highly chlorinated pool, rinse, or splash water)

• Contacting the public health department

• Clarification and elimination of the causes of contamination (checking/regulation of auxiliary hygiene parameters)

• Release of the pool after normalization of the free chlorine concentration (a temporary concentration of 1.2 mg free chlorine/l is permitted)

• Follow-up test for E. coli with subsequent success control

Pseudomonas aeruginosa is naturally present in water and is an extremely undemanding germ. It multiplies mainly where water stagnates. It contributes to the formation of biofilms in pipes and on the walls of swimming pools, in which it offers itself and other water germs (e.g. legionella) good protection against disinfectants and other influences.

Pseudomonas aeruginosa can cause serious inflammation in humans, for example of the ear canal or eye. If the upper DIN 19643 value for Pseudomonas aeruginosa of 0 CFU/100 ml is exceeded, the following measures are recommended (source: Federal Environment Agency):

• Immediate cessation of bathing operations

• Filter flushing with subsequent inspection

• Check the target specification (scheduled cleaning of the splash water tank or the pool floor and pool walls)

• High chlorination of the pool water (documentation sheet for high chlorination)

• Filter disinfection (with highly chlorinated pool, rinse or splash water)

• Follow-up inspection (release of the pool or contacting a specialist company)

• Contacting the public health department

• Clarification of the cause of contamination

Legionella is a type of bacteria that occurs naturally in water and can multiply particularly well in warm water. There is a health risk to humans if they inhale aerosols containing Legionella. This can lead to severe pneumonia (legionellosis). Baths with aerosol-forming devices that are operated at higher water temperatures (>23°C) are therefore a particular focus about Legionella contamination. If Legionella is detected in the filtrate or pool water, the following measures should be taken depending on the Legionella concentration (sources: DIN 19643, Federal Environment Agency):

• Immediately close the pool to bathing

• Carry out filter flushing

• Check filter flushing and optimize if necessary

• Check whether the last cleaning of the splash water tank, the pool floor and the pool walls has taken place as planned (target specifications)

• Carry out and document high chlorination of the pool water (documentation sheet for high chlorination)

• Carry out filter disinfection (e.g. with highly chlorinated pool, rinse, or splash water)

• Arrange a follow-up test for Pseudomonas aeruginosa

• If the follow-up test is inconclusive: release the swimming pool

• If follow-up test or subsequent routine samples are conspicuous:

  Contacting a specialist company/engineering office

  Contact the public health department

  Clarify the cause of the contamination (have it clarified)

Substances containing chlorine are generally used to disinfect bathing water, as these are easy to determine on site. Even small concentrations that are harmless to the user have a rapid effect against microorganisms. To ensure sufficient effectiveness, the free chlorine must not fall below a certain concentration in the bathing water. Likewise, for reasons of minimisation and the formation potential of by-products, a certain concentration should not be exceeded.

The following values apply if the standard range for free chlorine according to DIN 19643 is exceeded or not reached:
0.3 mg/l – 0.6 mg/l (normal pools)
0.7 mg/l – 1.0 mg/l (hot whirlpool pools, with and without ozone)
0.2 mg/l – 0.5 mg/l (for pools with additional ozone stage)

Recommended possible measures:

• Manual measurement of the chlorine content
• Calibration of the measurement and control system
• Renewal of the chlorine measuring cell
• Setting the pH value
• Cleaning the pool

A disinfectant containing chlorine can form a chemical compound with organic substances such as sweat, urine or skin residues in the bath water. This produces what is known as combined chlorine, which consists of chloramines. Chloramines are primarily responsible for the typical swimming pool odour. At high concentrations in the pool water, they can cause irritation of the mucous membranes, especially the eyes. A subgroup of chloramines, the trichloramines, can trigger asthma attacks in small children who are exposed to them. Elevated measured values for combined chlorine can be an indication that the chlorine dosage has technical defects or that more organic substances have been carried into the bathing water.

If the upper value of DIN 19643 for bound chlorine of 0.2 mg/l is persistently or repeatedly exceeded, the following measures are recommended:

• Make bathers more aware of the need to thoroughly cleanse their bodies before swimming (intensify signposting)
• Add powdered activated carbon or add H-carbon as an upper layer to the filter material (alternatively: install a downstream sorption filter with activated carbon in the bypass)
• Adjusting the pH value
• Increasing the fresh water supply
• Increase the addition of chlorine (higher redox voltage causes better oxidation)
• Checking / optimising the filter flushing

The use of chlorine-based disinfectants in the presence of organic substances in the bathing water can lead to the formation of trihalomethanes (THM) as an undesirable by-product. Humans can absorb THM on the surface of the water via the respiratory tract. THMs are suspected of having a carcinogenic effect. At higher concentrations, they can also cause toxic damage to the liver and kidneys in humans.

If the upper value of DIN 19643 for THM of 0.02 mg/l is exceeded several times or significantly, the following measures are recommended:

• Make bathers more aware of the need to thoroughly cleanse their bodies before swimming (intensify signposting)
• Add powdered activated carbon or add H-carbon as an upper layer to the filter material (alternatively: install a downstream sorption filter with activated carbon in the bypass)
• Adjusting the pH value
• Increasing the fresh water supply
• Increase the addition of chlorine (higher redox voltage causes better oxidation)
• Checking / optimising the filter flushing

If the filling or supplied fresh water contains bromide (seawater or brine or thermal water), bromate can be formed in combination with ozone or chlorine during bath water treatment. Bromate has kidney-damaging and carcinogenic properties.

If the upper value of DIN 19643 for bromate in bathing water of 2 mg/l is exceeded, the following measures are recommended:

• Determination of alternatives to bromide-containing filling waters
• Dilution by adding water with a lower bromide content
• For ozonation: consider alternative processes (depending on the pH value, ozone can favour bromate formation; at lower pH values (e.g. ≤ 7.2), bromate formation is slowed down)

Chlorite and chlorate can enter the bath water as by-products of chlorination. The danger of these salts is that they can damage the red blood cells in humans and hinder oxygen transport in the body (in people with certain metabolic disorders). They can also block the incorporation of iodine into the thyroid gland and lead to an enlargement of the thyroid gland.

Chlorite and chlorate in chlorine containers cannot be removed by bath water treatment. The individual contents of chlorite and chlorate in the pool water are added together and shown as a total in the measurement logs. Due to the oxidative conditions in the pool water circuit (redox voltage >750 mV), only chlorate will usually be found, as chlorite is spontaneously converted to chlorate.

If the upper value according to DIN 19643 for the sum of chlorite/chlorate of 30 mg/l is exceeded, the following measures are recommended (source: Federal Environment Agency, DIN 19643)

• Increasing the fresh water supply
• Check the storage conditions of chlorine containers (sodium hypochlorite solutions from the trade), at a maximum of 20°C, dark and without UV light influence, stored for no more than 3 months
• Installation of decentralised dosing stations
• On-site production of sodium hypochlorite (electrolysis)
• Do not allow the pH value in the storage tank to fall below 10.5
• No stock for high chlorination

Aluminium is the main component of flocculants, which contribute to effective filtration and the removal of unwanted pollutants and contaminants in the pool water. Flocculants are retained in the filter systems. Nevertheless, aluminium can get into the pool water, e.g. if the pH values are unsuitable and the reaction time for the formation of the flocculants is insufficient. Increased aluminium levels in the pool water can be an indicator of a need to optimise treatment.

If the upper value according to DIN 19643 for aluminium of 0.05 mg/l is exceeded, the following measures are recommended:

• Testing the pH value in the raw water before and after flocculant dosing
• Testing the acid capacity in raw water
• Testing the filtration speed (max. 30m/h)
• Check / regulate the flocculant dosing system and regulate the addition of flocculant (min. 0.05 g/m3)
• Use of a flocculant with higher alkalinity (> 65%)
• Testing / relocation of the reaction section for flocculants

The pH value is used to measure the alkaline or acidic character of an aqueous solution. The disinfection effect is directly related to the pH value. As the pH value increases, the disinfecting effect of the chlorine decreases.

If the pH value falls below or exceeds the measuring range of 6.5 – 7.2 according to DIN 19643 (for flocculation with aluminium-based agents, including aluminium-iron mixed products), the following measures are recommended:

• Manual measurement of the pH value
• Calibration of the dosing or measuring and control system
• Checking the flocculant dosage
• Addition of pH-value lowering or raising agents
• Testing / regulation of the acid capacity in the raw water

The acid capacity is a measure of the effectiveness of the flocculation process and the stability of the pH value. A sufficient acid capacity is important for the neutralisation of additives that are added to the bath water circuit. The minimum acid capacity values in the bath water depend on the alkalinity of the flocculant.

If the minimum values according to DIN 19643 of basicity < 65% minimum value of 0.7 mmol/l basicity ≥ 65% minimum value of 0.3 mmol/l are not met, the following measure is recommended:

• Addition of sodium hydrogen carbonate (“baking soda”) or sodium carbonate (soda) to the raw water

The redox voltage provides information about the disinfection performance in the pool water. This parameter is of considerable importance for assessing the disinfection effect of the added agents. In the pool water, the redox voltage depends on the concentration ratio of the disinfectant to the organic impurities. If more disinfectant is used (consumed), the redox potential decreases. It is also dependent on the pH value. The higher the pH value, the lower the redox potential at the same chlorine concentration.

If the redox voltage falls below the lower value according to DIN 19643 of ≥750 mV, the following measures are recommended:

• Testing / manual measurement / regulation of the chlorine content
• Testing / manual measurement / regulation of the pH value
• Testing / cleaning the redox measuring electrodes
• Testing / implementation / optimisation of filter flushing
• Make bathers aware of the need to thoroughly cleanse their bodies before swimming (intensify signposting)
• Checking the regular cleaning of the pool floor and pool walls