Septic tanks & wastewater treatment plants

Septic tanks and wastewater treatment plants in Australia

Updated 4 November 2026

Septic tanks in Australia cost about A$134 to A$4,225, and household wastewater treatment plants about A$4,278 to A$7,133. These prices are for the tank or plant listed, and they change with size and approval. To find the right size and an approved unit for your site, describe the household on BlaBlaPrice and compare local offers.

State rules and approvals

Rules are set state by state. In South Australia, septic tanks must meet AS/NZS 1546.1. Queensland's plumbing and wastewater code refers to the same standard. In New South Wales, household treatment units must hold current NSW Health accreditation, and an approval to operate is needed. In Western Australia, a unit must be approved under the state code for onsite wastewater systems before it can be sold.

Permits and what to check

Permit rules and costs differ for every state, so check the rules for the location before you buy. Ask whether the unit has approval for your state, and whether your warranty depends on an approval to operate. Systems must be designed and installed under state and local regulations and Australian Standards.

Season and seasonal use

Summer runs December–February and winter June–August. For a holiday house used only in summer, size the tank for the people who stay in those months rather than for the whole year. Installing in November gives you the weeks before summer for the groundwork.

Sizes, litres and people

Tanks are sold by litres and often by the number of people they serve, for example an 18-person 4,800 L tank. Types differ too: a three-chamber 2,500 L tank and a 7,300 L reed bed serve the same house in different ways. Treatment liquids and tablets start from about A$38, and a 12-month supply of enzyme product is listed from about A$190.

What to write in your request

Give the number of residents, whether the home is permanent or seasonal, the soil and water conditions, and the volume you need in litres. Add the make and model if you have one, whether you need installation, the site address and your budget in A$.

BlaBlaPrice is free for buyers. Describe the job in your own words in the chat, and add a photo of the site if you have one. BlaBlaPrice's AI asks for missing details, looks through sellers' websites and price lists in Australia, and shows the prices and businesses it found. Sellers registered on BlaBlaPrice reply in the chat with their own offer. Your contacts stay hidden until you decide to share them. For pipes and fittings, see plumbing or building and renovation, or create a request on the home page.