How to Prevent Your Underground Rainwater Tank From Floating

Posted on: 12 April 2018

Serious damage can be done to your underground rainwater tank if it floats up from the hole into which it was installed. Several measures can be taken during the installation to prevent such hazards from happening. This article discusses some of those preventive measures which you should discuss with the installer before your tank is delivered for installation.


The manufacturer of the rainwater tank can supply you with deadman anchors which you can use to hold the tank down when it is installed. These anchors are so heavy that it will be nearly impossible for any force, such as groundwater, to force the tank to float up. Alternatively, you may need to have concrete hold-downs made to secure your tank into the ground when it is installed. The anchoring system should be carefully designed or selected so that it is appropriate for the capacity of the tank.

Adequate Cover

Another way to prevent rainwater tanks from floating later on is by making sure that they have been covered adequately. This is usually achieved by backfilling the hole into which the tank has been placed. Have the backfill material compacted carefully (to avoid damaging the tank accidentally) so that it can hold the tank in place firmly. Cover the tank entirely, or at least cover most of its surface area.

Use of Ballast

You can also prevent tank flotation by placing some material inside the tank during the installation so that the tank can stay firmly on the ground while you complete the installation procedure. For example, you can pour some water into the tank so that the backfill material doesn't force that tank upwards during the installation. You can also use other heavy solids as ballast. However, this option can create more steps because you will have to remove those materials once the installation is completed.


Groundwater is usually the biggest culprit when tank flotation occurs. This risk factor can be managed by using pumps to get rid of any groundwater which collects in the excavated hole where the tank is to be installed. Keep the pump running until you have backfilled the tank. Make sure that you use a pump which will not be clogged by the muddy water being removed.

You may not need to implement all these measures as you install your underground rainwater tank. Talk to an expert and select the options which are most appropriate for your specific application.