Types of septic systems: which one your site needs, and what each costs
Updated
The short answer
The main types of septic systems are conventional gravity ($6,100 – $15,600 for 3 bedrooms), chamber ($5,800 – $15,000), low-pressure dosed, mound ($11,700 – $28,200), aerobic treatment units ($8,800 – $21,400), drip distribution and sand filters. The soil decides which ones your lot can use; the cheapest system that passes the soil evaluation is usually the right one.
Septic system types compared
All septic systems use a tank to separate solids. What differs is how the effluent is treated and dispersed afterwards, which depends on how well the soil absorbs water and how far it is to the water table or bedrock.
| Type | 3-bedroom cost | Needs a pump? | Upkeep |
|---|---|---|---|
| Conventional | $6,100 – $15,600 | No | Pump every 3–5 years |
| Chamber | $5,800 – $15,000 | No | Pump every 3–5 years |
| Low-pressure dosed | $9,000 – $22,800 | Yes | Annual inspection; pump and floats |
| Mound | $11,700 – $28,200 | Yes | Annual inspection; pump and floats |
| Aerobic (ATU) | $8,800 – $21,400 | Yes (unit or dosing) | Service contract; air pump, chlorine |
| Drip | $10,700 – $24,600 | Yes (unit or dosing) | Annual inspection; pump and floats |
| Sand filter | $12,800 – $30,700 | Yes | Annual inspection; pump and floats |
Planning ranges from the site's cost engine for 3 bedrooms at typical soil and average labour, including the perc test, design and permit. Not quotes.
Conventional and chamber systems
A conventional system is a tank plus gravel trenches with perforated pipe, fed by gravity. It's the cheapest and simplest system and needs no power, but it needs good soil: permeable enough to absorb water, and deep enough above groundwater and rock to treat it.
A chamber system replaces the gravel with open-bottomed plastic arches. They're lighter to install, work where gravel is scarce, and many states allow a smaller field for chambers than for gravel. Where a conventional system is allowed, a chamber system usually is too.
Low-pressure dosed systems
A pump sends effluent into small-diameter pipes under pressure, in doses, so it spreads evenly across the whole field instead of overloading the first few feet of each trench. It's used for marginal soils, shallow sites and fields uphill from the house. It adds a pump chamber, a pump, floats and an alarm — and the electricity and maintenance that come with them.
Mound, aerobic, drip and sand filter systems
When the soil can't do the treating, the system has to. A mound builds the field up above ground with imported sand. An aerobic treatment unit pumps air through the sewage so faster, oxygen-loving bacteria treat it before it reaches the soil. A sand or media filter passes effluent through a lined bed of sand or textile before dispersal. Drip distribution spreads effluent through small tubing just below the surface, which suits shallow soils and slopes, usually after pre-treatment.
All of these cost more to build and to run, and all of them need regular professional maintenance. Many counties require a maintenance contract for them.
Other systems you may come across
- Cesspools — a pit with open sides and no separate field. No longer permitted for new construction in most states and being phased out in some.
- Holding tanks — a sealed tank with no outlet, pumped whenever it fills. Used where no system can be permitted; pumping costs make them expensive to live with.
- Constructed wetlands — a lined bed of plants and gravel that treats effluent. Rare, mostly rural and regulated case by case.
- Composting and incinerating toilets — remove toilet waste from the system but still need an approved way to handle other wastewater.
How the type is chosen
You don't pick a system type from a list. A soil evaluation or perc test is done where the field will go, and the results — absorption rate and depth to a limiting layer — together with lot size, setbacks and local rules decide what can be permitted. Ask the health department or a soil scientist who isn't selling the install which types your results allow; the answer sets most of your budget.
Frequently asked questions
- What is the cheapest type of septic system?
- A conventional gravity or chamber system, at about $5,800 – $15,000 to $6,100 – $15,600 for 3 bedrooms — if your soil allows one.
- What is the best type of septic system to install?
- The simplest one your soil and county will permit. Fewer mechanical parts means lower running costs and fewer things to fail.
- What is the most efficient septic system?
- Aerobic units and media filters produce the cleanest effluent, which is why they're required near lakes and on tight sites. They're not the most economical — they use power and need servicing.
- What is the newest type of septic system?
- Advanced treatment units that remove nitrogen, and textile or peat media filters, are the main developments. Some states now require nitrogen-reducing systems in sensitive coastal areas.
- Is there a septic system that doesn't need a drain field?
- A holding tank, which is pumped when full, and some aerobic systems that spray treated water instead of using trenches. Every other system needs somewhere for the water to go.