When septic is your only option

A septic (on-site wastewater) system is required when your property is not connected to a reticulated sewer mains. This is common on rural properties, acreage, and some fringe suburban blocks. If you can connect to sewer, you generally must — most states require connection where it's available. If you can't, you need a council-approved wastewater system before a building permit can be issued. The septic system is a prerequisite for the building permit on a non-sewered property, not an afterthought.

The five system types compared

Common types include: conventional septic tanks with absorption trenches (the simplest and cheapest, but needs suitable soil and adequate space), aerobic treatment units (ATUs) that treat effluent to a higher standard for surface or subsurface irrigation, sand filters for higher-quality treatment, mound systems for poor-draining soil or high water tables, and composting toilets (for black water only, with grey water handled separately). The right choice depends on soil, water table, lot size, the number of occupants, and the council's requirements.

Council approval: what and how long

A septic system requires approval from your local council (or, in some states, a water authority) before installation. You'll need a wastewater design — usually prepared by a plumber or wastewater consultant — that shows the tank, treatment method, and disposal area (trenches, irrigation, or mound). The design must meet state EPA requirements for setback distances from boundaries, watercourses, and groundwater bores. The approval process typically takes 4–8 weeks once a complete design is submitted.

Land area, soil and setbacks

Septic systems need space: the disposal area must be set back from buildings, boundaries, watercourses, and groundwater bores by specified distances (often 10–100 metres depending on the system and state). Small lots may not have room for a conventional absorption trench system. A wastewater assessment early in the process confirms whether your lot can support a system and which type. If the lot is too small or the soil too poor, an ATU or mound system may be the only option — at higher cost.

Maintenance: the ongoing obligation

Septic systems require maintenance: periodic pump-out of the tank (every 1–5 years depending on use and type), inspection of the disposal area, and for ATUs, quarterly or annual servicing. Some councils require a maintenance agreement and periodic reporting. Budget for ongoing operating costs — a neglected septic system fails, blocks, and can contaminate groundwater and waterways, leading to enforcement and costly remediation. A septic system is not 'install and forget'.

Black water vs grey water

A septic system handles all wastewater (black water from toilets and grey water from sinks, showers, laundry). Some properties use a composting toilet for black water and a separate grey water system for the rest. This can reduce the septic system size, but the grey water system still needs council approval and proper design. See our grey water and off-grid guides for the combined approach.