How much does a septic tank system cost?

There is a wide variance in the cost of different sorts of septic tank systems. The cost of a system will also vary according to the size and location of your property, as well as whether a pump is needed.

Having said that, as a rough guide, supplying and installing a basic septic tank for a family home is likely to cost around $10,000 to $12,000. Installation should also include preparing, designing, and implementing an absorption trench system in which wastewater can safely run.

Again as a rough guide, the supply and installation of a wastewater treatment system might cost between $15,000 to $20,000. The cost will also vary depending on the size of your dwelling and the physical layout of your property.

The cost of supply and installation of a sand filtration septic tank system is likely similar to that of a wastewater treatment system.

What is a septic tank?

A septic tank is a tank or chamber at a basic level in which household sewage runs for treatment. Tanks are usually made from plastic, or fibreglass or concrete. They are connected by drain to the household waste and need an outlet in which the septic runoff or effluent can drain. 

A septic tank must be first filled with water. This water contains bacteria that help break down the waste. That waste is then decomposed within the septic tank by repeated processes of settling. The faeces generally split into multiple layers. A hard crust forms on top of the water. This crust is known as a scum blanket. At the bottom of the tank, more solid material known as sludge gathers. The wastewater gathers between the sludge and the blanket. Eventually, too much sludge will accumulate, and that will need to be pumped away.

When might you consider a septic tank?

You might have to consider installing a septic tank or septic tank system in a property if that property is not connected to the main sewage system. This commonly occurs on properties on the far-urban fringes of cities or towns or rural properties. In NSW, for instance, up to 20 per cent of all regional properties are estimated to have some form of on-site sewage management system, such as their septic tank system.

Alternatives to septic tanks

There are some alternatives to installing a septic tank and some additions that you might want to consider for a septic tank system.

One alternative is for the installation of a wastewater treatment system. Such a system is generally more expensive than a septic tank system - often as much as double the price. But it has advantages. Treated wastewater can be used on gardens and otherwise around the property - potentially a great benefit in a climate so vulnerable to drought. Wastewater treatment systems typically add a second tank or treatment process to the primary septic tank system. In this second tank, the wastewater is treated with additional disinfectants. 

A second alternative is the installation of a septic tank with a sand filter. Again, this option is typically more expensive than a more basic septic tank system. But the extra layer of filtering ensures the septic runoff is that much cleaner and safer than if the sand filter were not in place. With a sand filter, effluent travels through an extra layer of sand and rock. Water that emerges from a septic tank with a sand filter can generally be used in irrigation systems. This means that, depending on your needs, the extra expense for a sand filtration septic system may be economical for you in the long or even medium run.

These more expensive septic alternatives might be more appropriate if you live in an environmentally sensitive area. Indeed, they might also be required by your local government or other relevant development approval authorities.

What does septic tank installation involve?

Conscientious installation of a septic tank system involves a certain amount of hard labour and knowledge of local planning and environmental laws and regulations, and a keen consideration for topography and design.

An installer will need to have gained approval from local authorities before installation. They will need to have devised a plan for the run-off, making sure not to send the run-off too close to a water body, for instance. Once the plans have been developed, the installation will generally involve digging a hole for the tank to fit underground and then also preparing a trench absorption system for the run-off to flow to. 

Risks in septic tank installation

There are serious risks inherent in a septic tank being incorrectly installed or not maintained well after installation.

Contact with effluent carries health risks for humans. If the effluent emerges from the septic tank without being sufficiently treated or broken down and makes contact with humans, outbreaks of serious illness such as dysentery can occur. One way in which effluent can expose humans to such risk is if it is allowed to leach into a nearby stream or creek without yet having been sufficiently broken down.

Another risk is if the septic tank is not sealed correctly at the top. In this case, animals or insects may make contact with untreated waste, and in turn, infect nearby humans.

Regulations around septic tank installation

Australian states, territories and local governments have made many rules and regulations about most aspects of the septic tank installation. You should, of course, make contact with your local environmental and planning authorities before attempting the installation of a septic tank. Or, if you do not, you should hire someone with experience in negotiating septic tank regulations.

Regulations will typically cover issues such as the size of your septic tank system, the type of materials it should be made, and where wastewater can be dispersed. Regulations will generally prohibit wastewater from running too close to a water system unless treated to a higher standard.

Water treated to a higher quality - such as through a sand filtration system - might be allowed to be used for certain types of irrigation. It might even be allowed to be used in flushing toilets or washing machines. 

Generally, approval from a local council is needed before the installation and operation of a septic tank system. 

Maintenance tips for septic tanks

If you already have a septic tank, you’ll know that active and careful maintenance of your septic system is just as important as correct installation. If not, here are a few things you might want to consider when planning your septic tank maintenance.

• Be careful about what chemicals run into the tank. Chemicals that are too strong act as germicides (such as strong cleaning substances) before they could kill the bacteria needed for your septic tank to work properly.

• Try not to put too many oils, fats or food scraps straight into the system.

• Get expert advice on how often you should desludge your tank. Generally, a desludging is needed every three years.

• Inspect the system annually