Septic tank or AWTS? Which system suits you
Answer three questions and find which on-site system fits your block.
Septic tank with a trench, or an aerated system (AWTS)? The choice paralyses people, and installers each push their own. But the decision comes down to a few objective factors: your soil, your block size and whether the council allows a trench.
Answer three questions and we'll tell you the technically right option and why. No product to sell — just the correct reasoning.
The core rule: if your soil drains well and the block is big enough, a conventional septic tank with a trench is cheaper and simpler; if the soil is tight/wet or the block is small, you'll need an AWTS that irrigates. Either way, council approval is required.
Whatever the outcome, get a soil/percolation assessment before you buy: it has the final say on what your ground can take.
FAQ
When do I need an AWTS?
When the soil drains poorly (clay, high water table) or the block is too small for an absorption trench, or the council requires a higher treatment standard.
Do I need council approval?
Yes — every install or replacement needs council approval in every state, and design follows AS/NZS 1547.