Inflow and Infiltration (I/I) is a major problem facing water authorities and the Australian community, with costs running into millions of dollars and excessive amounts of energy wasted in transporting and treating unwanted water. 

Sewerage networks are typically designed with a contingency to allow for inflow and infiltration, and it is not unusual for storage systems to be added to existing sewerage networks to increase capacity to cope with inflow and infiltration, particularly during rain events. 

While these contingencies result in large and more costly infrastructure and pumping systems, many water authorities still report increases during normal rain events of between five and ten times average dry weather flow (ADWF), which overloads these systems.

With many water authorities wanting to work towards achieving zero environmental impacts and zero carbon emissions, addressing inflow and infiltration both in new constructions, as well as repair and rehabilitation of existing assets, is increasingly important. 

The benefits of addressing I/I include:

  • Reduced operation and capital costs
  • Lower power consumption and CO2 emissions
  • Reclaiming network capacity (supporting increased urban infill with existing infrastructure)
  • Less wear and tear on pumps, pipes and assets
  • Reduced potential for overflow
  • Less potential for formation of voids and associated damage to assets and surface structures
  • Lower insurance and litigation risks
  • Reduce pressure on already stretched workers 

While it may not be practical to completely eliminate I/I, it is possible to easily identify catchments and assets that are significant contributors, even with limited budgets or personnel. 

It is also necessary to realise that I/I management is a long term strategy involving a combination of assessment and repairs. 

Delaying starting the process (which can occur as the problem seems insurmountable), will only translate into a more costly program down the track; because leaks don’t get better on their own.

Failing to address prevention in new infrastructure through improved products and design methods will also only add to the I/I load later on.

Often, wastewater network field crews already have a good idea as to which catchments are regularly affected, with existing pump station data able to easily identify opportunities to start the I/I control process. More detailed investigations and modelling can be used to further refine I/I management priorities.

Innovative solutions are available to cost effectively reduce I/I and address the range of causes.

While many projects have been effective to reline damaged pipes and reduce I/I, sewer manholes generate a disproportionate amount of I/I and as such can be used to help quickly reduce I/I costs effectively.

ISC Services have put together free informative downloads to help water authorities better understand the sources and causes of inflow and infiltration, to help with urgent repairs and ongoing management.

Click here to find the below guides:

  • Inflow and Infiltration – A Practical Guide 
  • Introduction to Leak Testing of Sewers 
  • Environmental and Financial Benefits of Inflow and Infiltration Control

This is a sponsored editorial brought to you by ISC Services, for more details go to

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