The Houtrust waste water treatment plant (WWTP) was originally built in 1967. It was partially renovated in 1988 and 1995 to meet the (environmental) demands of that time. Even so, around 2005 the treatment plant was showing its age and was no longer capable of effectively treating the waste water flow from the homes and companies in The Hague. Moreover, the plant could not meet the more stringent European requirements for nitrogen removal. This was sufficient reason to totally refurbish this waste water treatment plant.
In 2007 and 2008, the Houtrust WWTP was drastically renovated. With the current treatment capacity of 430,000 pollution equivalents (p.e.) the plant is able, now and for a long time, to treat the waste water from the residents and companies of The Hague and surrounding areas. On a site that covers 5 hectares, the Houtrust WWTP can treat on average almost 79,000 cubic metres of waste water a day, in other words the capacity of more than 2,600 trucks.