Clear water is when rainwater or other interfering sources enter the wastewater system. These interference sources can be of different kinds, for example

  • Private connections (unused private PAC discharge basin)
  • Network failure
  • Connection error on a construction site in progress

Parasitic clear water poses problems at various levels, in particular for the dimensioning of the network, the creation of overloads and overflows, the risk of premature wear and tear of the pipes or the decrease in the purification yield and therefore the increase in the cost of treatment. These different problems are common to all networks.

Moreover, as the segregated network is still incomplete in Fully and rainwater infiltrates poorly in the plain because the water table is already very high, a large part of the rainwater ends up in the wastewater network.

We would therefore like to limit them as much as possible. But in order to do this and take appropriate measures … we still need to know where this water comes from and how it enters the network!

Thus, the municipality is looking for a solution that will allow it to identify the locations where parasitic sources and parasitic clear water are added to its network.


In Fully, various solutions have already been tested to try to find these sources, without much success. Indeed, the tested solutions gave a vision of the network at a precise moment and at a limited number of locations, and did not allow a continuous vision, necessary to be able to find the sources of parasitic water at the moment when the intrusions occur.

In the case of Fully, flow measurement is therefore rather problematic, for the following reasons:

  • The price and maintenance requirements of the measuring instruments available on the market make it impossible to deploy them on a large scale, so it is difficult to have an overview and to be able to detect the inflow of clear water throughout the network
  • The measurements obtained are very noisy, with sometimes a weak correlation between the measured level and the estimated flow. The work of post-processing and interpretation of the data is therefore quite substantial
  • Water level measurements are subject to caution, particularly due to the configuration of the lowland network, on flat areas and in places with small diameters (160-200 mm).

We would therefore like to see inexpensive and efficient solutions for measuring flows in the wastewater network, ideally continuously, so as to get as accurate an idea as possible of the various inputs and thus be able to detect and limit the inflow of parasite water.


  • Continuous measurements: not necessarily very precise, but allowing orders of magnitude to be obtained
  • Simplicity of the post-treatment stage
  • Intelligent analysis of available data
  • Cost
  • Definition of precise zones for sensors, to avoid simply placing them at entrances
  • Mobile and autonomous


  • Normal” flow map
  • Wastewater statistics
  • Results of the latest measurement campaigns


Olivier Studer

Head of IS Department Fully

Municipality of Fully

Rue de l’Eglise 46
1926 Fully

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The municipality of Fully has about 9,200 inhabitants for 3,779 ha. Agriculture is thus particularly present with 1’155 ha. The commune’s water networks are managed by the Services Industriels de Fully.