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Does My Tank Need To Be Underground?

Posted by Callum Vallance-Poole

The first GRAF plastic underground tank was launched in 1978 and plenty has happened since then. A high standard of quality in production is an essential foundation for unique products. This ensures the good stability and precision fit of the individual components. We have even developed a new, unique production process for the Carat underground tank. GRAF manufactures first-class products: resilient, precision-fit and easy to use! With GRAF rainwater tanks, vehicles can park over the site and pedestrians can walk over making them perfect for small spaces.

Now you’ve decided that you want to save money on your water bill and help the environment, you need to decide where to put your rainwater tank. GRAF offers rainwater tanks that can be situated above or below the ground. Read on to find out which is best for you. 

Underground Tanks – Pros & Cons 

Rainwater has so many uses in and out of your home, storing your water underground means it’s hidden away and out of sight. A lot of people prefer this as water tanks often aren’t aesthetic and can be very large structures.

However, installing a tank underground can be pricey and installation will take longer. 


  • Saves Space – Placing your rainwater tank underground saves space. If space is limited, especially in private homes, underground water tanks can be located under driveways or lawns.
  • Hidden Away – Above-ground water tanks can be an eyesore whereas underground water tanks can be neatly hidden away from view. With our tanks, we have versions strong enough to take pedestrians and vehicle weight.
  • Vandalism – Water stored underground is safe from potential vandals and tampering.
  • Fire Protection – Underground tanks offer protection from fires and other natural disasters
  • Animal Damage – If you want to locate your underground tank on a farm or nature reserve, underground tanks offer protection from potential damage by animals.
  • Corrodes Slower – Underground tanks deteriorate much slower, particularly if you are using a metal tank. This is important especially if your water tank will be hooked up to an auto-fill system, as any leaks that develop could easily go undetected for weeks otherwise.
  • Safer – Tanks underground often have restricted opening This is ideal if you have young children and pets.


  • Cost – Underground water storage tanks can be pricier than above-ground tanks as they’re more durable and the construction technique is more specialised.
  • Installation – You may need to hire help to install your tank as they often need to be placed deep underground. This whole process takes longer than an above-ground tank.
  • Extras – A pump is needed to extract water from underground storage tanks, while above-ground tanks may only require gravity to provide enough pressure, especially if a water tank stand is deployed.

Extra Features

Underground tanks will need extra features in order to make them safe. 

  • Good pre-tank or in-tank filtration of 0.5mm or less
  • An overflow trap to exclude foul odours from the drains
  • A backflow protection device (non-return valve) on the tank overflow
  • A pump that is reliable and equipped with a fine suction filter
  • A pump that can easily be extracted from ground level
  • A secure child-proof access cover

GRAF supplies both below and above-ground systems. The above-ground systems are very much different from the underground tanks, which are designed to be UV stable. This helps to protect them from ultraviolet lights, along with temperature fluctuations to help keep the water in an underground tank to a suitable level and keep it a much better quality. 

It is very much advised to purchase an above-ground tank if you’re looking at this avenue and not looking to install an above-ground tank in an above-ground situation. 

Inbetween Solution

With some tanks, you can partially bury them in the ground. You can usually bury a poly water storage tank underground up to 1 meter. You will need to dig your hole at least 12 inches wider than the diameter of your tank and prepare the standard foundations for them. Be sure the ground is compacted well and is level, so you have a flat base for your tank. Once you place the tank in the centre of the base, you can fill your tank with water and fill in the surrounding area with compacted crusher dust and cement (3 parts to 1 part). Do it slowly, no more than 10cm at a time. When completed, you may want to put a fence around the tank to help protect it from outside interference.

Wherever you decide to place your water storage tank, you need to be sure to do some research, get some expert advice, and do it right the first time, so you don’t waste your time and money. These projects are not quick fixes and require proper maintenance, even if you have a water storage tank underground and out of sight.