Installations of below-deck and underground tanks
Have a look through our photo galleries of recent installations and get an idea of what's possible. A bladder tank may be the solution beneath a low back deck, or a true underground tank may prove ideal to save space or get the tank out of sight. Size can be anything from 1600L, although an underground tank becomes better value as it gets larger.
For examples of tanks installed above ground see slimline tanks or round tanks
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Two 7000L bladder tanks were fitted side-by-side under this large timber deck roughly 8 x 6m in size. The deck was designed to have wider than average spans by using larger cross-section timber, and was a minimum of 700mm above the ground which allowed for 7.0 x 2.0m bladders to be fitted underneath.
A bladder only rises to 500 or 600mm depending on type so may not be able to utilise all the space available.
A bladder only rises to 500 or 600mm depending on type so may not be able to utilise all the space available.

With steel supports to a raised ground floor this East Fremantle home was ideal for a bladder tank. The Ecosac tank fits inside a 300mm high tubular steel frame wrapped in geotextile, which holds the tank in place and allows it to rise to 600mm when full rather than the 500mm of some other models.
The fill pipework is relatively complex compared to other water tanks as the bladder as no overflow and the sealed bag must not be overfilled
The fill pipework is relatively complex compared to other water tanks as the bladder as no overflow and the sealed bag must not be overfilled

Tank made in 2 halves and joined onsite to form a single leakproof unit. Reduced shipping volume makes for an attractive price.
This unit is configured for installation below ground. A vertical length of 100mm DWV pipe in the centre is adequate to prevent an sagging in the top, and access is through this raised inspection opening. Can be linked to create a greater volume.
Easy to move into location, and ideal for below ground or semi-buried below a raised floor or deck
This unit is configured for installation below ground. A vertical length of 100mm DWV pipe in the centre is adequate to prevent an sagging in the top, and access is through this raised inspection opening. Can be linked to create a greater volume.
Easy to move into location, and ideal for below ground or semi-buried below a raised floor or deck

On a site such as this with relatively little space between the house and the boundaries the tank is generally installed after the slab has been completed and before brickwork starts. Here the slab was reinforced along the edge as the tank is so close.
The tank takes all the downpipes from around the house and must therefore be set lower in the ground to give that pipe sufficient fall. An extension riser then brings the lid up to just below final deck level, where a removable hatch will give access. Overflow goes stright into the soakwells to be installed just next to the tank
The tank takes all the downpipes from around the house and must therefore be set lower in the ground to give that pipe sufficient fall. An extension riser then brings the lid up to just below final deck level, where a removable hatch will give access. Overflow goes stright into the soakwells to be installed just next to the tank

The telescopic riser is used to maintain access into the top of the tank when the burial depth is increased. Here a garage is to be built over the tanks and so the depth of cover has been increased.
Replacing the green plastic lid shown on the nearest tank with a cast iron lid (see Inset) in conjunction with the 700-1000mm burial depth allows vehicles up to 3.5 tonnes to drive over the tank.
Replacing the green plastic lid shown on the nearest tank with a cast iron lid (see Inset) in conjunction with the 700-1000mm burial depth allows vehicles up to 3.5 tonnes to drive over the tank.

This client in Wembley wanted to add a tank as large as possible to their battleaxe block. We used the Graf EcoBloc system here which comes into its own with tank sizes over 15-20kL.
A retention tank retains the water inside for future use. A detention tank on the other hand is designed to hold the water temporarily to slow discharge into a soakwell or other drainage system and prevent surges.
A retention tank retains the water inside for future use. A detention tank on the other hand is designed to hold the water temporarily to slow discharge into a soakwell or other drainage system and prevent surges.

The retention tank is wrapped in a thick waterproof membrane supplied in roll form with the seams welded onsite. The black poly membrane is protected inside and out from abrasion or puncturing by a strong geotextile layer. The inner layer can be seen here.
Inlets and outlets are via flanged fittings welded into the liner.
Inlets and outlets are via flanged fittings welded into the liner.

This 8 x 4 x 1.8m tank is constructed of stacked 250 plastic modules. Around 97% of the total tank volume can be used for water storage. These slack together for shipping making for a very compact.
The inner geotextile layer can be seen beneath the base, and the plastic membrane is resting on the sids of the pit and will be folded over when the structure is completed - like wrapping a parcel.
The inner geotextile layer can be seen beneath the base, and the plastic membrane is resting on the sids of the pit and will be folded over when the structure is completed - like wrapping a parcel.

The final stage of installation - the tank is backfilled and compacted and then covered with a minimum 500mm of soil. Soakwells will then be installed (roughly under the Bobcat) to take the tank overflow and surface runoff. The area will later be concreted.
The front door of the house is roughly where the guy is using the hand-held compactor - so the tank fills the entire driveway.
The front door of the house is roughly where the guy is using the hand-held compactor - so the tank fills the entire driveway.

If there's enough headroom then either Coerco's 4500L or 9000L low round tank can be used as cost-effective storage. The apex of this tank roof is only 1820mm. The tank was dropped into the basement before the roof was put on.
We do also have rectangular tanks that can be built in-situ if there's no opportunity to get the tank in beforehand.
We do also have rectangular tanks that can be built in-situ if there's no opportunity to get the tank in beforehand.

This 1200mm high poly tank is one of the few designs that's suitable for low-profile installations.
Five tanks are linked together at the base here to form a 5500L tank taking water from almost 200sqm of house roof and supplying most of the house with rainwater.
Water inflow is split between two tanks to minimise the chance of overflow in heavy rain.
Five tanks are linked together at the base here to form a 5500L tank taking water from almost 200sqm of house roof and supplying most of the house with rainwater.
Water inflow is split between two tanks to minimise the chance of overflow in heavy rain.
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