Air Gaps | Tank Plumbing | Rain Harvesting by Blue Mountain Co


Air Gap is an essential element in any Rain Harvesting system where your overflows are plumbed into stormwater. Air gaps prevent stormwater backflow from entering your rainwater tank and lowering your water quality. They also create a visual inspection point for detecting any overflow issues and stop mosquitoes and other vermin from entering your rainwater tank.

Product Families
Air Gap
Air Gap
Air Gap
Air Gap
  • Benefits of Air Gaps
    • Prevent stormwater backflow from entering your tank and contaminating your rainwater,
      which could happen to you, without you knowing about it.
    • Mosquito-proof your tank and stormwater pipes
    • Keep frogs, rats and other pests out of your tank and stormwater pipes
    • Create a visual inspection point for detecting any overflow issues
    • Easily maintain thanks to removable upper and lower screens
    • Protect stored rainwater quality
    • Easy to Paint
    • Easy to Install
  • Air Gap FAQs

    How does backflow occur, and how does an air gap help?

    In an extreme rainfall event there is the possiblity that water can back up through the stormwater overflow pipe and towards the rainwater tank.

    If your local stormwater infrastructure (beyond your property boundary) becomes blocked, the system can “charge”, causing dirty stormwater to surge back through your stormwater pipework. If your rainwater tank overflow is connected to stormwater, this “charged” stormwater can backup into the tank.

    If the pipes connected to the overflow of the rainwater tank are crushed, excess water from any pipework connected to the same system could flow back towards the tank, taking with them whatever debris is in the system.

    If your tank is going to a soakage pit, in an extreme rain event the pit could become saturated and water can flow back up towards the

    An air gap prevents this problem by creating a physical gap between your rainwater tank and stormwater lines. With an air gap, overflowing stormwater is prevented from backing up into your tank. Instead, it will spill out through the front of your air gap.

    My screens keep falling out. What should I do?

    Check that the bayonet fitting is engaged correctly. Push and turn the top filter to secure the screen in place.

    Should I install my air gap at the top or bottom of the overflow?

    You can install your air gap at the top or bottom of the vertical overflow pipe. Installing your air gap closer to the top of the overflow will generally make it easier to maintain.

    We recommend ensuring you don’t have a charged line which could effect the height of installation.

    Can I plumb 100mm pipe into a 90mm air gap?

    You can connect the downstream (bottom) side of your air gap to a 100mm pipe with the use of a 100×90 socket reducer. Please consult a licenced plumber for suitability in reducing the upstream (top) connection to your air gap.

    The overflowing water from my tank is spilling out the front of my air gap. How can I fix this problem?

    Overflowing rainwater from your tank can begin leaking from the air gap if the bottom screen becomes dirty or obstructed. To prevent this problem, regularly check and clean your bottom screen.

  • Photo Gallery

The Rain Harvesting steps addressed:

Learn more about applying the 8 Rain Harvesting steps.

Find out more

Rain Harvesting Design Service™

We'll design your Rain Harvesting system - for free!

Your selection

Add Rain Harvesting or Plumbing products to your list.