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The process of threshold treatment involving the addition of WTP H307S in drinking water was originally used for stabilisation of calcium carbonate in hard waters, thus preventing scale formation with increased temperature. A similar addition of WTP H307S is now widely used for corrosion control in soft waters.

Corrosion results in many problems, one of the most important being the discolouration of water, known as red water. Discolouration of a similar kind can also be caused by precipitation from solution of naturally occurring soluble iron compounds. Threshold treatment with WTP H307S can be used to control the discolouration arising from either cause.

Mechanism of Protection by H307S

Protection depends on the formation of a very thin film, usually containing iron and calcium although other bi-valent metals may replace the latter. This film is cathodic in character i.e. it suppresses the release of electrons at cathodic areas on the metal and is impermanent, it needs to be kept in a state of good repair therefore by the constant supply of fresh inhibitor.

Water Supply Systems

As many applications are in municipal supplies the effect of phosphate on the potability of the water is of great importance. DWI approves the use of polyphosphates and silicates. All the components of WTP H307S are food or potable grade.


  • When beginning treatment up to 15 ppm should be used to build up the protective layer quickly.
  • When treating water to prevent corrosion of cold water supply mains, 50 ppm as product is proposed.
  • It is recommended that the treatment is pumped proportional to water flow and that the dosing pump is set up to give small doses of chemical at as high a frequency as is practical.
  • A silicate test kit is available (WTP TK146) for a reserve of 3-5ppm at 50ppm dose or a WTP H307S test kit for product concentration (WTP TK107).
Please refer to material safety data sheet for detailed handling/storage instructions.



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The above information is believed to be correct but does not purport to be all inclusive and shall be used only as a guide. The company shall not be held liable for any damage resulting from handling, contact, mis-use or mis-application of the above product. In all instances the user should satisfy themselves that this product is suitable for the anticipated application and should carry out suitable and sufficient risk/COSHH assessments and a method of use statement.

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