Underground Water Storage Tanks

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When space and accessibility are an issue, an underground tank is the answer, especially in an urban environment.

An increasingly popular option for architects and builders is an underground water tank. This allows for homeowners to maximise their space giving them more green space/or parking, when placed under paved traffic areas, driveways, garden beds or lawns, this solutions is not only aesthetically pleasing but an eco-friendly way to capture and harvest rainwater. With the smallest environmental footprint in the industry, Polymaster underground rainwater tanks give you the maximum capacity for the minimum square metreage. Designed using Finite Element Analysis (FEA) and Australian-made from UV-stabilised polyethylene, the range covers 3,300L and 5,000L capacities with optional vortex filter and pump configurations. Backed by a 15-year design service life and a 10-year manufacturer’s warranty when installed to specification.

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3,300Ltr Underground Water Tank

URT3300B

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3,300ltr Underground Water Tank with Vortex Filter

URT3300VF

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3,300ltr Underground Water Tank with Vortex Filter & Garden Pump System

URT3300VF/GP

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5,000ltr Underground Water Tank with Vortex Filter underground water tanks for filtered rainwater collection

3,300ltr Underground Water Tank with Vortex Filter & Pump

URT3300VF/PC

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5,000ltr Underground Water Tank

URT5000B

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5,000ltr Underground Water Tank with Vortex Filter

URT5000VF

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5,000ltr Underground Water Tank with Vortex Filter & Garden Pump System

URT5000VF/GP

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5,000ltr Underground Water Tank with Vortex Filter & Pump

URT5000VF/PC

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The Polymaster 5000L Underground Water Tank is a premium water-harvesting solution engineered for urban environments, new home builds, and properties with limited above-ground space. Designed by geotechnical experts using Finite Element Analysis (FEA), this tank is built to withstand significant ground and water pressure, making it one of the toughest underground poly tanks on the Australian market.

Why Choose the 5000L Underground Tank?

This tank is the “out of sight, out of mind” solution for homeowners and builders aiming for a 6-star energy rating. It provides a massive 5000L capacity while remaining completely hidden, keeping stored water cool and protected from algae growth, and freeing up your backyard for better use.

Food Grade

Food-grade polyethylene, certified to AS/NZS4020, the Australian standard for drinking water

Quality Assurance

Polymaster is certified for the international standard for quality management ISO9001

Product Certification

Standard AS/NZS 4766:2006 for peace of mind. Licence no. BMP657671 & BMP650824

Find Your Local Distributor Store

Polymaster’s round rainwater tanks are available across Victoria, South Australia, New South Wales, and South-East Queensland. As leading Australian storage tank manufacturers, we offer round poly tanks in various sizes to suit rural, residential, and industrial applications. No matter your location, we have a round water storage tank solution to suit your needs and budget.

I am proud to supply this feedback as it has been a long time since I was treated so amazingly well as a customer until I dealt with Polymaster. A) received excellent Pre Sales & Service from your dealer, Martha at Electel. B) Then 10 days before delivery I received a positive call from a polite young lady who ran through the complete scope of the order. To say I was appreciative was an understatement. Wished more companies had your service commitment / DNA. C) Then a day before delivery I received a polite phone call from a truck driver who introduced himself as your driver and ran through the logistics / offloading etc. Said he couldn’t give me an exact time but would ring me in morning to advise exact ETA. I have never met a truck driver who was so organised. All of the above culminated in to me being blown away with Polymaster’s outstanding customer service. Thank you very much and please pass my feedback onto your Mgr Director. It was a pleasure to deal with a company who is so transparent and organised, congrats.

G.C

Callignee, VIC

From entering details online and then talking with Tony Columbro to ensure I had details correct to then the text messages when the tank was ready. Then notified it was loaded and on its way to its new home. The whole process was professional and super smooth. Love the tank.

H.M

Nyah, VIC

Once tank was ordered it was confirmed and outlets checked . Delivery day was advised and driver was excellent . Great company to deal with.

D.P

Hepburn Springs, VIC

Good communication from Polymaster and delivered without a problem. Very happy with the quality of Polymaster products too.

Anonymous

Thanks to the driver, Bruce for delivery to a spot made difficult by recent rain. Managed to get tanks to their right spots. Good effort!

Anonymous

Sales people were excellent in providing updates to delivery and delivery driver also keep me informed of delivery times and helpful with information regarding the tank.

A.G

Great customer service especially Rachel. Also the driver was extremely helpful and professional in his handling of his job. Tank arrived on time as promised. The only little thing is that the tank was not put on position but close for us to push it the the foundation. Definitely we will order our next tank from them. Just recommended my friend to buy from Polymaster.

Anonymous

Good price. Great communication. On time friendly delivery service. Brilliant. Oh and the product is second to none.

G.O

Very happy with the product, also very happy with all the text messages telling me how the production was going. Will definitely be buying another tank from you in the future.

K.S

Besides the delivery arriving a day early the entire experience was excellent. Tim was excellent and did everything possible to help out to make sure the tanks were put in the best place. Thanks very much."

A.J

Loch, VIC

Ecstatic with delivery made by Mark Sinclair today - haven't had good old service like this in a very long time. Mark was polite, helpful & an absolute bloody gem. Highly recommend Polymaster to everyone.

C.C

Scarsdale, VIC

Easy to deal with. Prompt delivery. Courteous and friendly delivery driver. Great experience."

B.E

Table Top, NSW

My experience was excellent. I don't know how it could be better. Everything worked exactly as I hoped.

I.S

Second Valley, SA

The customer service was fantastic with a step by step walk through on the setup of the tanks. The recommendations on how to get the best set up of the tank fittings pump positioning. To the delivery of the tanks and the positioning on the ground.

Ben

"From start to finish it was nothing but a great experience. Very professional. Great company with great staff."

Anonymous

Over the moon with the quality of the tanks and the service ????

S.O

Burra North, SA

Both truck drivers are excellent. Very helpful. All tanks are wonderful. Very quick delivery after placing order. Had phone calls from Polymaster to check tank details and progress of delivery.

Neil Winter

Murgheboluc, VIC

"Great customer service from office, keeping me up to date with delivery time etc. Delivery man mark was on time, knowledgeable and did a fab job getting in a tight driveway. Very happy with my tank thank you."

Kerry Marsh

Ocean Grove, VIC

First class service. First class product.

Anonymous

We’ve found working with Polymaster to be a positive experience. The quality of the products which we have used has been very high, and the willingness and technical capacity of the staff to tackle non-routine engineering modifications has given us confidence in the finished build.

P. Baker

Land Energy Pty Ltd

The decision to sell Polymaster tanks to my customers is an easy one due to the fact that I strongly believe they are the best quality tanks on the market and I can confidently stand by the product I am supplying.

David Hartwig

Plumbing Contractor

We are very pleased with the choice we made to go with Polymaster due to the quality and excellent service. We will endeavour to use more Polymaster tanks as we continue to upgrade our property.

Matthew

Bridgewater SA

How do underground water tanks work?

Underground poly tanks store rainwater in a buried tank fed by an inlet from your roof. Water is delivered to your taps or garden either by gravity or a submersible electric pump with optional mains changeover. The setup includes a distribution outlet, an overflow to stormwater to prevent flooding, and an access riser/drain for inspection and cleaning (often with a vent and level gauge). Being underground keeps water cool and protected, reduces visual impact, and frees up usable yard or driveway space.

How can I clean an underground water tank?

Do periodic checks via the access riser: clear leaf traps/filters, flush sediment if present, and follow Polymaster’s installation & maintenance guidance (use licensed trades for confined-space work). This keeps water quality and system efficiency high.

How do you install an underground water tank?

Step 1. Trench excavation: Excavate to spec with ~300 mm working clearance, safe battering, and a firm, level, compacted crushed-rock base.
Step 2. Placement of tank: Lower via lifting lugs, set on the base, and level in both directions with feet stable.
Step 3. Placing water in tank: Pre-fill to the specified volume to stabilise the tank and counter buoyancy if groundwater is below the midline.
Step 4. Backfilling: Backfill evenly in ≤300 mm layers with 7 mm minus/type b crushed rock, hand-compact without stressing the tank.
Step 5. Plumbing of feed and overflow pipes: Install the inlet and overflow with ≥1% fall; connect the overflow to the stormwater with an accessible non-return valve.
Step 6. Mounting of the self-cleaning vortex filter urvf01: Mount vertically with adequate fall near the downpipe or beside the tank; connect per spec.
Step 7. Plumbing up the submersible pump: Fit supplied pump fittings and lifting chain, connect discharge to outlet, and any mains changeover device.
Step 8. Wiring the pump and pressure switch: Mount the controller/pressure switch, run cable in conduit, and have a licensed electrician complete wiring.
Step 9. Inspection and servicing: Inspect and pressure-test for leaks; schedule periodic cleaning and function checks of filters and internal parts.
Step 10. Landscaping and commissioning: Cover and finish with paving/landscaping; ensure the lid is sealed and commission the system.

The underground rainwater tank system must be installed by a qualified plumber/installer. Installation by a non-licensed person may void the warranty. All wiring must be performed by a licensed electrician. Follow the Polmaster underground water tank installation guide to ensure you have a successful installation.

How do I pump water from an underground tank?

Install a submersible pump (Polymaster kits include options) and, if desired, an automatic mains changeover for easy supply to the home or garden.

Can slimline water tanks go underground?

No, use purpose-built underground models engineered for soil/traffic loads. Slimline tanks aren’t designed for burial. Polymaster provides dedicated underground SKUs and installation specs for this use.

How long do underground water storage tanks last?

Polymaster’s underground water storage tanks have a 15-year design service life and a 10-year manufacturer’s warranty when installed.

Get in touch

Call Polymaster today on 1800 062 064

Contact our team Find your local store

When space and accessibility are an issue, an underground tank is the answer, especially in an urban environment.

View All Products

Why Choose the 5000L Underground Tank?

Highest Quality & Standards

Food Grade

Quality Assurance

Product Certification

Find Your Local Distributor Store

What Our Clients Say

Underground Water Tank FAQ's

How do underground water tanks work?

How can I clean an underground water tank?

How do you install an underground water tank?

How do I pump water from an underground tank?

Can slimline water tanks go underground?

How long do underground water storage tanks last?

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