HDN neutralising filters

Choose from a wide range of neutralising filters for the conditioning of water produced by desalination installations. Use these filters for improved taste and prevention of corrosion in your fresh water system.

Low pH

Water with a low pH value, such as product water of desalination plants (both evaporators and reverse osmosis type water makers), often is corrosive and tasteless. This so-called ‘acid condition’ is due to the presence of free carbonic acid gas (CO2) and lack of natural minerals.

Neutralising / mineralising

To make this water neutral or slightly alkaline, it should be neutralised or mineralised. To ensure complete removal of CO2, the water can be filtered through a bed of neutralising filter media, named “EWT compound”. In the low pressure filtration process, the CO2 reacts with the EWT compound to natural bicarbonates and calcium (Ca2+). Both ions will contribute to less corrosive water.

EWT compound

In the past, it has been common practice to use marble neutralising (mineralising) though the reaction is slow and equilibrium is difficult to reach and maintain. EWT compound is now preferred due to its quick and complete action. Its special structure makes it rapidly and uniformly soluble.

EWT compound is a granular medium, packed in 25 kg bags. The average consumption of material is 1 kg (2 lb) on 70 m3 of water. It is sufficient to partially refill a few times per year in order to replace the material that has been dissolved in the water in due process. Upon refilling, the filter must must be flushed by reversing the water flow in order to remove dust and contamination from the fresh filling material. We would furthermore advise you to occasionally flush the filter in order to loosen the filter bed.


The HDN GRP filters are made of 100% composite fiberglass corrosion-resistant material with a polyethylene inner shell and are corrosion resistant.


The HDN GRP filters are supplied with PVC-U piping and manual (three-way) ball valves for full operation, including backwash of the neutralising filter. The piping diameter is dependent on the filter model.