The quality of drinking water in the Netherlands is excellent. Nonetheless, this quality can deteriorate between the water production site and the client. One of the key water-quality issues in the distribution network is the risk of water discolouration. The causes of water discolouration are the introduction of particles during water treatment, the ‘production’ of particles in the distribution network, and the accumulation of particles in the network; in the event of a hydraulic disruption, the resuspension of the particles can occur, which leads to water discolouration.
This project involves the development of a tool to determine the risk of water discolouration for an entire neighbourhood, as well as the location of the greatest risk of discolouration in the neighbourhood. Water companies will then be able to target their cleaning programmes much more precisely. This will result in cost-savings and a better management of the risk of water discolouration.
Preventing water discolouration
Solutions for the prevention of water discolouration can involve 1) measures related to water treatment (limiting particle introduction), 2) the installation of self-cleaning networks (preventing particle accumulation), and 3) timely cleaning (limiting the amount of sediment that can be resuspended) (Vreeburg 2007). For existing networks, the third solution – network flushing – is the most economical.
The effective flushing of the distribution network is done from a clean-water front, at a velocity of 1.5 m/s, and using flushed volumes three times the content of the main. To prioritise their network flushing programme, water companies currently still make frequent use of a combination of water discolouration complaints and the Resuspension Potential Method (RPM) (Mesman and Meerkerk 2015). This approach has several drawbacks. First of all, the number of RPM measurements is limited. Moreover, the measured values are very location-specific, and often do not represent the entire neighbourhood. We expect that we’ll be able to eliminate these drawbacks with a discolouration prediction tool.
Developing a discolouration prediction tool
The final product of this research project is a discolouration prediction tool that water companies can apply in their own supply areas. The tool will give water companies insight into which locations become discoloured the fastest, and where measures (e.g., flushing, redesign into self-cleaning networks) will be most effective.
The tool can be used to establish guidelines for the optimisation of water company flushing programmes. This would for example include determining strategic locations for RPM measurements. The tool can also contribute to knowledge for the design of a (secondary) mains network, in which water quality is also taken into account.