PAWS standard

The UK pool industry operates  to a set of guidelines which are not in compliance to with German DIN standards and standards applied throughout most of Europe. The German DIN standards are well established  and comprehensive, however modifications are now required to the water quality parameters to reflect new analytical techniques and water treatment strategy. In addition, the DIN standards  do not encompass air quality, Dryden Aqua have therefore propose a modification to the DIN water quality standards, biological standards and have encompassed air quality to form a new standard referred to as PAWS, Pool Air & Water Standard.

Pool water quality is very important, but from a chemical toxicological perspective of air quality is just as important. The air quality above the surface of the water will be dictated by the water quality and the ventilation system.

Air quality

Air quality is important for the health and wellbeing of the public as well as the staff working in the facility. With regards to the staff, pool operators should have a COSHH risk analysis for the facility and include in that risk analysis the air quality.  There are European Standards for air quality, referred to as WEL`s, Work Exposure Limits. Pool operators therefore have a legal requirement to monitor and record atmospheric conditions for pool disinfection by-products such as ;

  • Nitrogen trichloride
  • Chloroform
  • Cyanogen chloride

Water Quality

The DIN standard does not include some basic water quality parameters and a range of toxic disinfection by-products identified by Dryden Aqua

Biological water quality

Biological water quality relates to the analysis of the water for specific bacteria. In addition to this analysis Dryden aqua that the water is also checked by RLU relative light units as a measure of ATP ( adenosine triphosphate) ATP is not a measure of bacteria but rather a measure of bacterial cell biomass in the water treatment loop.  Standard bacteriological analysis will usually give a low to zero reading. The analysis takes 3 days to complete and as such if high readings are detected,  the public will have been exposed to the bacteria for at least 3 days.  Dryden Aqua propose that ATP analysis is conducted on the water.  The results are achieved in a few minutes and it gives a very accurate indication if there is a biological risk associated with the pool.

Parameter Water AnalysisUK swimming pool guidelines DIN normPAWS
pool air & water standard

DAP Factor, average for mg Chlorine used per bather per day

typically 6 to 12


 Typically 4 to 6

<4  with target <2

New water quality parameter set by Dryden Aqua

THM`s (chloroform in water)2


<100 ug/l

< 20 ug/l

< 20 ug/l

Cyanogen chloride (cyanide)


<50 ug/l


< 20 ug/l

Analysis provided by Dryden Aqua, only local pools to Edinburgh at the moment.

Total combined chlorine (in water)

Less than half the free chlorine level


<0.2 mg/l

<0.1 mg/l for inorganic  trichloramine.

<0.5 mg/l for organo-chloramines

Water sample should be treated with EDTA to remove metal interference

Free chlorine

0.5 to 3 mg/l


0.3 to 0.6 mg/l

0.3 to 0.6 mg/l


Chlorine dioxide

<0.4 mg/l

0.05 mg/l

Chlorite mg/l

<0.2 mg/l

<0.7 mg/l


not defined


<50 mg/l

Chlorate has a low toxic level


not defined


>100 mg/l

Guideline applies to freshwater pools



<1.0 ntu

<0.1 ntu

<0.05 ntu

Close pool above 0.2 ntu

Hardness as Calcium

40 to 150 mg/l

150 to 500 mg/l


>100 mg/l as Ca2

Colour Pt/Co


 <15 mg/l 


<15 mg/l


Alkalinity as CaCO3

75 to 200 mg/l



60  to 120 mg/l





<100 mg/l

Guideline applies to freshwater pools



<250 mg/l


<25 mg/l

Guideline, non-critical, high levels cause turbidity, gypsum scale, and may damage concrete


7.2 to 7.8

6.5 to 8.5

6.5 to 7.6

6.9  to 7.2



<0.2 mg/l

>0.05 mg/l

0.02mg/l to 0.1mg/l

Critical parameter for optimum water quality.

TDS ( total dissolved solids)

1000 mg/l above influent water



<1000 mg/l (recommendation)

Guideline non critical



<0.2 mg/l

<0.02 mg/l

<0.01 mg/l







Dryden aqua test kit

Permanganate value mg/l



<4 mg/l

< 4 mg/l,

Less than 4mg/l above influent mains water.

Dissolved oxygen


>75 % sat


100 % +/- 2 %  of saturation

Measurement after the filters, indicates anaerobic conditions, or gas super-saturation.





<0.1 mg/l

Mains water supply under 0.1mg/l, alarm if above 0.5mg/l





<10 mg/l

Close pool above 50 mg/l

Langelier index




-0.5 to +0.5







Total coliforms

<10/100 ml

<1 / 100 ml


< 1/100 ml

Bathers must shower before entering pool.

Pseudomonas aeruginosa 6 deg C +/- 1 deg C

< 50/100 ml

< 1/250 ml

< 1/100ml

< 1/250 ml

Good housekeeping must be applied to keep biofilm under control. Use DryOx

Escherichia coli 6 deg C +/- 1 deg C

< 10/100 ml

<1/250 ml

< 1/100ml

< 1/250 ml

Bathers must shower before entering pool

Legionella pneumophila 36 deg C +/- 1 deg C



< 1/100ml

< 1/100 ml

Can only occur in pools with biofilm

CFU ( Colony Forming Units) 37 deg C +/- 1 deg C



< 100 / 1ml

< 10 / 1 ml

RLU,  bacteria, endotoxins & exotoxins, by ATP analysis




<100 RLU/ml

Good <100, warning 100 to 250, take action, 250 - 500, close pool >500

Air Quality






Nitrogen trichloride

No limit, up to pool operator COSHH



<0.3 mg/m3

Upper limit 0.5 mg/m3





<0.1 mg/m3


Cyanogen chloride

0.77 mg/m3



<0.05 mg/m3

0.77 mg/m3 HSE limit upper 15 min exposure level.


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