Precast Concrete Retention /Detention Tanks – Absolute Concrete

Precast Concrete Retention /Detention Tanks

Customised Tanks in a range of sizes to meet your storm water retention and attenuation requirements..

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Absolute Concrete Precast Concrete Retention / Detention tanks to meet your design requirements. Bring us the design specified in your storm water report and we’ll customise a tank to meet your needs.

Tanks may be fully buried, completely out of sight so as not to disturb play areas or views.


      • Made with high slump certified concrete, it is a one piece moulded concrete tank that can be partially or fully buried up to 200mm underground.
      • A drive over Tank option is available suitable for light vehicle traffic.
      • A range of Pre Cast sizes are available to fit your plans.

Manufacturing standards

Absolute Concrete Retention Tanks are manufactured to standards NZS 3106 and use material that conform to NZS 3422and NZS 3109:1997.  They are manufactured using high strength concrete and fabricated circular steel reinforcement (welded steel mesh) not fibre like some other manufacturers.  This helps to achieve a water tank suitable for a range of installations.  The tanks have lifting anchors cast into the concrete walls.

A range of tanks are available to suit your situation:

Standard water tanks may be completely buried with a maximum of 100mm fill cover consisting of light free draining material such as bark, scoria or mulch.  Standard lids are designed for pedestrian traffic only.

Heavy Duty Tanks are available on request.  A heavy duty tank may be completely buried up to 200mm underground.  These lids are sealed on delivery.  Heavy Duty lids are designed to withstand either pedestrian traffic or we can cater for tanks that are required for wheel loads.

After installation of the water tank we advise that you make sure it is filled with water before backfilling.

For instances where the tank is designed to remain empty most of the time, a flanged anti-floatation base can be added.

Siting Instructions for Water Tanks

Our tanks are delivered using our trucks each with a 18 tonne crane positioned at the back of the
deck. The site for the truck to park to offload should be level and allow for the truck to back up to the
tank site. The truck must then be able to put out the outrigger/stabilising legs to extend a total of 3.0m either side
as per the photo below. The stabiliser legs can not be put onto soft fill, they must be supported
by solid ground. The truck cannot unload off the side or on uneven ground. The crane is able to
reach out approximately 3-4m from the rear of the truck depending on tank model and size and only
if these conditions have been met.

Rearward Tank Installation


Please make sure:

      1. There are no overhead wires, branches, gate posts, etc blocking the access of the loaded Tank and Truck. The driver will take as much care as possible not to damage property but will not be held accountable for damage due to restricted access.
      2. The ground is firm enough for the truck. Make sure there are no holes, drains etc to fall into. If you have a wet site please have a digger or appropriate machinery on site.
      3. Siting requires a level site and a good foundation so that all the weight is distributed evenly on solid ground. The truck will not be stable on fill. Please ensure the digging material has been placed so that access for truck and stabiliser legs is not restricted.
      4. Crane legs must be able to be extended on flat level ground that is solid virgin earth – not dirt fill – should the ground be deemed unstable it will be your responsibility to excavate and compact with hard-fill.
      5. Your tank site needs to be flat and level. It is advisable to set the tank onto a base of fines of 7mm granular material on top of level ‘Good Ground NZS3604’ should ‘good ground’ not be attainable, a base of compacted hard-fill material will need to be added. If there is any doubt that the fines may be washed out over time, it is advisable to box them in. The area should be free of rocks, tree roots and other protrusions that may cause pressure points.

Please have your site prepared for our truck as we allow 30 minutes per tank on site. Please note:
Site preparation is the purchasers’ responsibility however we are happy to carry out a site visit prior to
delivery to assist in your preparation. Any site work by our company will be at your cost and any delays on site due to circumstances outside our control are chargeable.