Monday, 1 May 2017

What type of Water Storage Tank is best - Concrete or Plastic?

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Concrete Tanks

Concrete water tanks and ferro-cement water tanks are generally strong and long-lasting. They are very heavy, and difficult to handle. 5000G tank would weigh about 8 tonnes. Concrete water tanks are most often installed underground however smaller tanks are available for above ground.

New concrete water tanks often impart tastes and may leach lime thereby increasing the pH of water. Accordingly these concrete water tanks may need to be flushed before use.



Concrete water tanks delivered on site in a complete form are craned off the truck and onto a prepared sand base. These tanks are sometimes in one to three pieces. Concrete sections are sealed primarily with a rubber or synthetic sealing ring or some form of sealant. Sealant is then applied to the inside of the tank at the join to stop the water leaking out.

Cracking and leaking is one of the most common complaints suffered by concrete tanks. As long as the tank can be drained, the cracks can be repaired. In some bad cases, a plastic liner is required, which can be very expensive.

The standard for concrete tanks allows for a certain amount of leakage, while the standard for plastic tanks does not allow any leakage.

Plastic tanks

The most popular type of water tank in NZ is the rotationally moulded Plastic Water Tank. These tanks have been made by some manufacturers using this process for over 20years. Plastic tanks and plastic liners must be constructed of materials that are at least of food-grade standard (compliant with AS/NZS 2070: Part 1 and Part 8 Australian Standards for Food Contact) and if the water is to be used for human consumption the plastic material must actually comply with the requirements of potable-water standard (AS/NZS4020: 2002 Potable (Drinking) Water Standard). The rotational moulding industry is one of the few industries that have a comprehensive standard that covers both the raw materials used, and the manufacturing and workmanship of the completed water tanks.



Polyethylene (Poly) is non-corrosive tank material designed for long life. Polyethylene will not rust or suffer from corrosion as will metal and concrete during their service life.   Poly tanks are lightweight and easy to handle – no heavy equipment needed.

Poly tanks are usually made in one single piece. They have no joints or seams where part of the tank has been welded together, and no sealants are used to join any parts of the tank together.

Promax only uses materials that comply with AS/NZS4766: 2002 Polyethylene Storage Tanks for Water and Chemicals that inhibits the growth of algae. Light transmission is a potential problem that fibreglass tanks have a need to manage.

Polyethylene tanks can be recycled at the end of their service life. Recycled plastic cannot make water tanks because potable water regulations only allow virgin plastics to be used. However, there are many other product applications for recycled plastic. The recycled plastic can have new sun and heat protection added, and go on to enjoy another long life.


The material your tank is made from is largely a matter of personal preference. Neither concrete nor plastic is an absolute winner. Plastic tanks are a lot more cost effective than concrete, longer lasting and easier to install.

Concrete Tanks

Concrete tanks are created by either a moulded (or precast) process or a plastered process. Promax plastic tanks are much stronger and more durable.




  • Can be buried underground. Aesthetically, burying removes what can be a blot on the landscape.
  • Keeps water cooler due to insulation value of concrete.


  • Your site needs to be accessible to a hiab or similar otherwise the tank will have to be built on site.
  • It is not easy to retrofit new outlets to the tank.
  • The tank may be damaged by earthquakes.
  • They are more expensive to buy and install than plastic tanks.


Plastic Tanks

Plastic tanks are made from UV-stabilised, food grade polyethylene.


  • Plastic tanks are easy to manoeuvre into position.
  • It is relatively straightforward to retrofit outlets.
  • Because they can flex a little, plastic tanks can withstand earthquakes.
  • They're a lot more cost effective than concrete tanks to buy and install.
  • Promax Corrugated tanks can be buried in to 1m in ground


  • Plastic storage tanks can't be fully buried however you can help to hide them with planting.


Repairs and Maintenance

Not surprisingly, as water tanks have been very common in New Zealand for many years, there is a whole industry devoted to repairing, maintaining and cleaning them.

Concrete tanks should be given a cement wash every few years to counteract the leaching of lime into the water.

Plastic Tanks require minimal maintenance apart from removing sediment build-up every few years or as required.

Other Considerations

When you put in a new tank you should think about how you will keep the water clean. Contaminants on your roof will be flushed into the tank, you should aim to minimise this by diverting the first flush of water away from your tank. There are many products that do this or you can create your own.