Stagnant water, a danger still unknown


Stagnant Water, a danger still unknown

Managers of buildings or of potable water distribution networks are required to provide users and citizens with quality drinking water. However, the presence of stagnant water in a portion of a drinking water system can represent a significant health risk.

Stagnant water is found in all drinking water distribution systems, in buildings as well as in aqueducts. Depending on the degree of stagnation, the water can have a viscous texture, be smelly or act as an incubator in the development of bacteria, including legionella. For these reasons, it is imperative to identify dead pipes in to eliminate any presence of stagnant water.

An audit of the drinking water network allows the identification of the sources of danger due to the presence of stagnant water. It is then possible to design solutions aimed at correcting a deficient and potentially dangerous installation.

Concrete examples

Every building evolves over time. These changes can directly or indirectly affect the plumbing system and thus contribute to the presence of stagnant water. Here are a few examples:

  • a conduct condemned following renovation work,
  • an application that is no longer in use, but remains connected to the distribution network, such as a concierge, a sink, or a fountain,
  • a bypass line in the event of an emergency,
  • a conduct between two adjoining buildings,
  • a closed-circuit mixed water network with little use, in particular the emergency showers,
  • a floor that is closed or undergoing major renovation for a long period or a hotel with a low occupancy rate during the off-season,
  • a change in the vocation of the building, such as the conversion of a commercial building that consumed a large amount of water into a condo building.

Municipal aqueducts are also vulnerable to the presence of stagnant water, mainly due to low flow. An accumulation can also occur in the following situations:

  • a pipe of a dimension greater than current needs to supply future residential complexes,
  • a bypass pipe shared between two municipalities and used in the event of an emergency,
  • an oversized network to meet demand in the event of a fire,
  • an unused portion of the network due to the closure of a plant in the territory.

In addition, in recent years, several initiatives have emerged to reduce water consumption, including the implementation of various programs to save the potable water and the installation of low-consumption plumbing components. These programs have their reason to exist, and the municipalities must continue their efforts in this direction. However, some of these systems help reduce the flow of water through the pipes, which can cause stagnation. Designers must increasingly take this into account when developing a network to promote the flow of water through the pipes of appropriate dimensions, without wasting it.


Various solutions aimed at eliminating stagnant water can be implemented. Here are some ideas:

  • have a precise plan of all the pipes in a distribution system and keep it up to date during repair work,
  • design looped distribution networks using a circulation pump,
  • create circulation loops for all types of water: cold, hot, process, etc.,
  • install water quality measurement probes measuring the amount of chlorine or any other unwanted particles,
  • drain the stagnant water pipes at regular intervals to allow water to circulate,
  • eliminate obsolete pipes following renovation work.

Modifications to a water system can be costly and difficult to achieve in an existing environment. The corrective measures must then be implemented project by project, depending on the level of risk assessed during the building analysis. Emptying the pipes is an easy and accessible means of prevention. This helps prevent water from stagnating in underused portions of the system and does not require any invasive work.


Increasingly aware of and concerned about the risks associated with the proliferation of bacteria in drinking water distribution systems, several North American organizations have been working on the subject. The NSF Group, which develops quality and safety standards, was working - in collaboration with a committee on which Health Canada sits - to develop Standard 444: Prevention of Injury and Disease Associated with Building Water Systems. This standard provides methodology covering the prevention of injury and disease from Legionella as well as other waterborne pathogens, chemicals, and physical hazards. This document will serve as a reference for designing safer water distribution systems for users.

Other problems are emerging, which cannot be ignored as they can affect the public health. Stagnant water in the pipes thus presents a significant risk.

Drinking water is increasingly becoming a priority issue for all levels of government, including municipal administrations. Many programs aimed at saving this resource have emerged in recent years. However, other problems are emerging, which cannot be ignored as they affect public health. Stagnant water in the pipes thus presents a significant risk. Sooner or later, plumbing and aqueduct engineers will have to rethink the design of drinking water distribution systems to take this aspect into account to provide quality water to all users.

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