Rainwater from your roof is the most common and cost effective method of water collection. Here we have listed everything we think you need to know about our 22,500L water tanks.


Standard Semi Buried Water Tanks are designed to be installed at ground level, Buried to roof level or Partially Buried (ensuring uniform depth of soil). They are not designed to be a retailing wall.

Site Preparation, the site loading of a full 22,500litre water tank is around 30 ton . This extreme loading requires total care to distribute the load evenly across the foundation of the Water Tank. Foundations must be good ground in accordance with NZS 3604.

The site must be free of all solid objects (rocks, tree stumps etc) and be flat and level. Firmly compacted consistently across the base where the tank will be placed.


  • 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.
  • Concrete tanks are designed to keep your water cold (up to 9 deg cooler than other storage methods)
  • Concrete tanks keep the water in the dark. This helps prevent algae growth present in some other tanks.
  • Concrete water tanks are a reliable and convenient water storage in the event of fire.
  • Concrete water tanks do not require additional restraints in high wind zones.
  • A Dart water tank does not require a building consent.
  • A trafficable tank option is available suitable for light vehicle traffic.

Manufacturing standards

Dart water tanks are manufactured to standards NZS 3106 and use material that conform to NZS 3422 and NZS 3109:1997. They are manufactured using high strength concrete and fabricated circular steel reinforcement (welded steel mesh). This helps to achieve a water tank suitable for a range of installations. The tanks have lifting anchors cast into the concrete walls, and in the floor of the tank for tricky installations

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. Width 3.5m Height 2.7m weight 10.5 ton.

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. Width 3.5m Height 2.8m plus a 200mm riser. Weight 11 ton.

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


Our tanks are delivered with a Hiab, each with a 15 ton crane positioned at the back of the deck. The site for the truck to park to offload must 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/stabilizing legs to extend a total of 10 meters. The stabilizer legs can not be put onto 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.

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 up to 30 ton. 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 the truck can access the site.
  4. Crane legs must be able to be extended on flat level ground that is solid virgin country – not fill, preferably in accordance with NZS 3604.
  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 and this should be on a base of compacted material. 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 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. Delays in truck waiting with incur extra costs to the purchaser.


Dart Septic Tanks are Manufactured in a range of sizes from 4500L to 6000L in the standard or Dual Chamber. They are also available in 10,000L and 22,500L for commercial applications.

Our Septic Tanks weigh upwards of approximately 4.5 ton and are able to be maneuvered on site by digger or alternatively dropped straight in the hole by our crane trucks.

Septic Tanks are manufactured to NZS3107:1997 and are designed to be buried with a maximum of 600mm fill cover. Standard tanks are designed to withstand pedestrian traffic only, however we can also manufacture tanks where wheel loads are required.

Single Chamber Septics:

Single chamber systems are suited for systems installed in light free draining soil. Once the waste is gravity fed into the tank, it settles and is filtered through a bio filter that filters out all the solids.

Pump Chambers:

Pump chamber systems are suited for systems installed where wastewater needs to be lifted higher. Suitable for high water tables.

Dual Chambers:

Dual chamber systems are suited for systems installed in heavy, clay type soil that will take longer to drain away. The two tanks allows the waste to settle before draining through the first filter, then settle again in the second tank before being passed through a second filter into the drainage field.


Retention tanks are designed to catch the storm water and 'retain' it in the tank for household use, any overflow is then usually run off to either the council storm water system or a soakage pit designed by an engineer.

Detention tanks are designed to slow down the flow of stormwater. The storm water enters the tank through an inlet and then trickles out through a small opening in the bottom of the tank, often referred to as an orifice.

Dart Concrete has the ability to manufacture your retention tank to the exact size as required by your engineer.


Dart Concrete Floodwash Tanks have been designed to maximise flow performance using our 22,500L precast concrete water tank. The tank pictured has an epoxy coated cast iron 300mm peak flow valve with 316 stainless steel shaft set into the tank providing a massive flow of water to clean your yard / feed pad. Alternative sizes are available on request.

Flood washing systems use surges of water to clean the yard. Washing times can be reduced to less than one minute. Use either fresh water, water from the plate cooler or storm-water or pump your effluent pond back up to your floodwash tank.
Floodwash tanks are capable of fitting a wide range of pipe sizes. They are fitted with strategically placed lifting anchors cast into the concrete, to allow for safe off-loading, and efficient and economical installation. We have secured the services of a specialised engineer to work out flow rates and valve performance.

Flush tanks by Dart Concrete are produced in accordance with NZS.3106:1997 They are manufactured in 40MPa concrete for high durability and each unit is water tested prior to delivery.


Dart Concrete manufacture and retail BioCycle wastewater treatment systems for BioCycle Systems Ltd. The BioCycle System is a complete package aerated wastewater treatment system suitable for domestic wastewater particularly for the lifestyle market.
The BioCycle System is distributed and installed throughout the north island via a network of registered installers.

For more information on the BioCycle System go to www.biocyclesystems.co.nz


Interceptor Traps produced by Absolute Concrete are essentially a Precast Concrete container that acts to capture and retain greasy and or oily fluids inside the unit between its multiple chambers. The grease and oil rise to the top of each chamber while the rest of the liquid passes beneath The interceptor trap may be supplied in a number of different sizes and capacities to match the required application and to conform with Local Authority regulations.

Interceptor Traps are designed as an addition to Cafes, Restaurants or Commercial Kitchens for the protection of wastewater treatment systems.
Interceptor Traps come in many sizes and configurations to suit a range of flow applications and regulatory requirements. They are fitted with strategically placed lifting anchors cast into the concrete, to allow for safe off-loading, and efficient and economical installation. Each unit is manufactured with either PVC or Earthenware fittings cast into the structure.


Manholes made by Dart Concrete have been used throughout the North Island of New Zealand for access chambers, in both stormwater and sewer applications, drop chambers, pipeline junctions, direction changes and attenuation tanks.

The Dart Concrete manhole system consists of precast concrete and cast iron components and offer proven performance. The system includes a range of manhole diameters and riser heights, as well as various concrete lid options, cast iron frames and covers, steps, joint sealants, clamps, and base options.

Precast manholes are also available as pump stations and come set up complete with macerator pump, high level float and alarm switch.


Dart Concrete manufactures a range of precast concrete Cesspits, available as Flat Top or with Back Entry depending on your requirements. These units are designed to suit regional infrastructure specifications for stormwater and help prevent unwanted debris blocking drains and make drainage systems less expensive to maintain.

Standard sizes available are:

  • 300mm x 300mm x 600mm
  • 300mm x 450mm x 740mm
  • 450mm x 450mm x 1020m
  • 450mm x 675mm x 1200mm


Dart concrete manufacture 900mm x 900mm porous well liners complete with 100mm thick precast lids with 100mm pvc pipe access points for the connection of downpipes.

Used typically within the Hamilton City region, two well liners serve approximately 40m2 of roof area for dispersal stormwater into the ground.


Dart Concrete manufacture a range of different sized pre cast concrete riser rings for lifting the level of manhole access.

Dart Concrete riser rings come in 100mm,150mm 200mm,300mm 600mm and 900mm all with 600mm diameter access openings.


Dart Concrete produces both L walls and T walls for containing feed silage.

These tip out walls offer a fast-track construction solution. The versatility of precast concrete wall panels lends them to a wide range of applications; livestock housing, grain stores, storage bays, silage panels and flood defence walls.

Concrete is used more than any other man made material for good reason; it is sustainable, durable offers superior fire resistance, gains strength over time and is affordable.


Dart Concrete manufactures a range of reinforced precast concrete stone traps. The largest one piece unit has been designed with a 2.2 metre entry to enable the wider tractor / loader buckets to clean with ease. The stone trap is designed to allow time for stones and gravel to settle out and ultimately reduce the wear and tear on your effluent pumps.