Water Quality Guidelines

Depending on the type of equipment to be cooled or how the temperature must be controlled, special requirements are placed on the cooling water in terms of its condition and cleanliness in order to protect the system from corrosion and deposits.

Depending on the type of equipment to be cooled or how the temperature must be controlled, special requirements are placed on the cooling water in terms of its condition and cleanliness in order to protect the system from corrosion and deposits.

the ingredients found in the water

the degree of contamination

the materials used

the type and size of the cooling or temperature control systems

Temperature control equipment/ maschines
Cooling circuits
Spray amount
  Temperatures of the surface wall or water9)Open8)(semi-)8) closed 
  t < 100°C100°C < t < 140°C140°C < t < 220°Ct < 60°Ct < 95°C 
pH-value 7 - 9,510)7 - 9,510)7 - 9,010)8,3 - 9,016)8,5 - 9,510)6,5 - 8,5
El. conductivity
(reference temperature 20°C)


200 - 200011)200 - 200011)200 - 200011)200 - 220016)200 - 200011)-
Total hardnessmmol/l20,20,20,9 - 6,2(2) 0,90
°dH12115,0 - 35(12) 51
Acidity KS4,36)mmol/l614)687,513)16)4-
Carbonate hardness°dKH3434452116)23-
Chloridesmg/l805030150(80) 5050
Iron Fe2)3)mg/l111116)10,5
Copper Cu2)3)mg/l0,50,50,50,516)0,50,5
Sulphate SO45)mg/l10070503251000,5
Total germ count7)KBE/ml10.00010.00010.000-15)10.000-15)
Solidsmg/ln/an/an/a< 1012)n/an/a


1) All values mentioned in this guideline refer to treated cooling water conditioned with a suitable treatment agent made available by gwk.

2) Iron and copper compounds can be dissolved in the cooling water and are insoluble. Levels of iron and copper in the cooling water
can provide information on corrosion processes in the cooling circuit as well as on possible deposits in the heat transfer media. Experience tells us that at the starting stage and during load fluctuations, increases in the iron and copper concentrations occur.

3) dissolved iron and copper compounds

4) Guideline values for the water quality of open evaporative cooling circuits in accordance with VDI 3803 and VDI 2047-2.

5) When using inhibitors, higher concentrations are permitted in individual cases (monitoring of the corrosion rate is advised).

6) Elevated acidity due to alkalinity of the inhibitor system.

7) When the germ count is above 10,000/mL—but never later—a biocide must be used in a closed/semi-open system, (discontinuous addition). Compliance with VDI 2047-2 is mandatory when using open cooling circuits.

8)open = re-cooling system with evaporation (cooling tower); semi-closed = closed, without pressure superposition, contact with  ambient atmosphere; closed = hermetically sealed from the surrounding atmosphere and superpositioned on pressure.
Carbon steel and non-ferrous metals. Mixed-metal-system. Irrespective of the mixed-metal-system, the use of unprotected carbon steel is only permitted by using an appropriate corrosion inhibitor.

9) The maximum system temperature is always the decisive factor.

10) In connection with the corrosion inhibitor ci 23 and ci 1300 cl, the upper pH value is 10.5.

11) In connection with the corrosion inhibitor ci 1300 cl, deviations to higher conductivities is possible.

12) If the the solids load is high, please consult with gwk.

13) When using hs 20, LSI should be < 2.5 and if hs 21 is used, LSI should be < 3.1.

14) LSI < 2.8
15) In Germany the requirements according to VDI 2047-2 and 42. BImSchV must be considered.
16) Value is complemented by gwk and/or adjusted for the treatment with products from gwk.

Furthermore, the following instructions apply:

  1. In systems with galvanized pipeline materials, a pH value of 8.5 must not be exceeded. The treatment procedure must be agreed upon.
  2. Systems with aluminium components must be considered separately. A special preparation process must be applied in order to achieve corrosion protection. However, during this process values may deviate from the data mentioned above.
  3. The addition of biocides may only take place after a sufficiently long interval before or after a discharge.

Additional water

The quality of the additional water must comply with the information provided in the current Drinking Water Ordinance (TrinkwVo).

These guide values provided by GWK are recommendations for the water/chemical operation of cooling and temperature control circuits. When compliant with the guidelines for the quality of the additional and circulating water stated above, essential requirements are met for the flawless operation of the products.

Based on our assessments, these guide values may deviate if the system conditions require it and a safe operation is ensured, nevertheless.

If the water quality is different, do not hesitate to contact us.



technotrans solutions GmbH
Scherl 10
58540 Meinerzhagen

Should there be deviations in the quality of the water causing faults or damage to the cooling or temperature control products, we can not assume any guarantee.