If your home is not connected to a town sewer system, the way treated wastewater is managed on your property is an important part of your overall wastewater system.

Many homeowners focus heavily on choosing the wastewater treatment tank itself, but the treatment system is only part of the solution. Once wastewater has been treated, it still needs somewhere suitable to go.

This is where the wastewater irrigation or land application area becomes important.

Two common methods used to distribute treated wastewater around a property are surface irrigation and subsurface irrigation.

While both systems are designed to disperse treated wastewater safely across an approved area of land, they operate differently and may suit very different properties.

The right option can depend on your soil, property size, slope, landscaping, household wastewater volume, local council requirements and the type of wastewater treatment system being installed.

Understanding these differences before purchasing or replacing a wastewater system can help homeowners avoid expensive changes later.

This guide explains how surface and subsurface wastewater irrigation work, their advantages and disadvantages, what homeowners need to consider and why the irrigation area should be planned at the same time as the wastewater treatment system.

What Is Wastewater Irrigation?

Wastewater irrigation is a method of distributing treated wastewater from an onsite sewage treatment system over or beneath an approved area of land.

For homes outside sewered areas, household wastewater generally needs to be collected, treated and then safely managed within the property.

An onsite wastewater system may receive wastewater from toilets, showers, baths, sinks, kitchens, laundries and other household plumbing fixtures.

After treatment, the resulting effluent is directed to an approved land application area.

In NSW, onsite sewage management systems and their associated land application arrangements are regulated through local councils. NSW Health also maintains accreditation requirements for certain types of domestic sewage management facilities, including aerated wastewater treatment systems, septic tanks and collection wells.

The purpose of the irrigation area is not simply to “get rid” of wastewater.

A properly designed land application system allows treated wastewater to be distributed in a controlled manner while protecting people, neighbouring properties, waterways and the surrounding environment.

The NSW EPA notes that appropriately managed effluent irrigation can reduce demand for other water sources and reduce pollutant discharge to waterways, but it must be managed in a way that protects both human health and the environment.

What Is Surface Wastewater Irrigation?

Surface irrigation distributes treated wastewater above ground.

Depending on the approved design, the treated water may be delivered through irrigation sprinklers or other approved surface distribution equipment located throughout the designated irrigation area.

When the treatment system reaches the appropriate operating level, a pump sends treated wastewater through the irrigation pipework.

The water is then dispersed across the surface of the approved irrigation area.

Surface irrigation areas are generally clearly identifiable on the property and need to remain suitable for wastewater disposal throughout the life of the system.

Homeowners therefore need to think carefully about where the area will be positioned.

It should not be treated like spare land that can later automatically become a pool area, shed site, driveway, extension, entertaining area or landscaped feature.

Changes to the property can affect how the wastewater system operates.

What Is Subsurface Wastewater Irrigation?

Subsurface irrigation distributes treated wastewater below the ground surface through specially designed irrigation pipework.

Instead of treated wastewater being sprayed above ground, it is delivered into the soil through underground irrigation lines.

These lines are normally installed within a designated land application area at a depth and spacing determined by the wastewater design and site conditions.

The exact system design will depend on factors such as soil characteristics, slope, expected wastewater flow and council requirements.

Subsurface systems can be attractive to homeowners because most or all of the irrigation infrastructure is hidden underground.

Once correctly installed, the area may look similar to the surrounding lawn or landscaped area.

However, just because the irrigation pipework cannot be seen does not mean the area can be forgotten.

It remains an important part of the wastewater treatment system and must continue to be protected from damage.

The Main Difference Between Surface and Subsurface Irrigation

The simplest difference is where the treated wastewater is released.

Surface irrigation distributes treated wastewater above the soil surface.

Subsurface irrigation distributes treated wastewater below the soil surface.

That single difference has a significant impact on installation, appearance, maintenance, landscaping and how homeowners use the surrounding area.

Neither option should automatically be considered better for every property.

The best solution is the system that suits the individual site and has been designed and approved for that property.

Why Your Property Determines the Irrigation System

Wastewater irrigation is not generally something that should be selected from a catalogue without considering the site.

Two homes with the same wastewater treatment tank may require quite different irrigation solutions.

A wastewater consultant or suitably qualified designer may consider factors including:

Soil type and soil depth.

The rate at which the soil can accept and manage water.

• Property slope.
• Available usable land.
• Household size.
• Expected daily wastewater generation.
• Location of buildings.
• Property boundaries.
• Driveways.
• Watercourses.
• Dams.
• Swimming pools.
• Bores.
• Existing landscaping.
• Future development plans.
• Groundwater conditions.
• Drainage patterns.
• The type and treatment standard of the wastewater system.
• Local council requirements.

This is why a wastewater or site and soil assessment can be such an important part of planning an onsite wastewater system.

The treatment tank and irrigation area should work together as one complete wastewater management solution.

The Importance of Soil

Soil plays an enormous role in wastewater irrigation.

Treated wastewater applied to land needs to be managed by the soil and vegetation without creating persistent saturation, uncontrolled runoff or other environmental problems.

Different soils behave very differently.

Sandy soils can allow water to move through relatively quickly.

Heavy clay soils generally behave very differently and may have slower infiltration characteristics.

Some properties can contain several different soil conditions across the same site.

For example, soil near the house may differ from soil further down the property.

This is one reason homeowners should be cautious about assuming that because a neighbour has a particular wastewater system, the same design will automatically work on their property.

Wastewater design should be property specific.

Advantages of Surface Wastewater Irrigation

One of the main advantages of surface irrigation is accessibility.

Because much of the distribution system is visible and accessible, faults may be easier to identify.

If a sprinkler becomes damaged or stops operating properly, the homeowner or service technician may notice the problem relatively quickly.

Surface systems can also provide flexibility when correctly designed because components can often be accessed without excavating underground pipework.

For some suitable properties, this can make maintenance more straightforward.

Another potential advantage is that the homeowner can easily see the designated wastewater irrigation area.

This can help remind everyone using the property that the area serves an important wastewater function and should not be built over or obstructed.

Disadvantages of Surface Wastewater Irrigation

The visibility of surface irrigation is also one of its disadvantages.

Not every homeowner wants sprinklers or irrigation equipment visible around the property.

Surface components can potentially be damaged by lawn mowers, vehicles, animals, garden equipment or general activity.

Homeowners also need to be aware that the area is being irrigated with treated wastewater, not ordinary drinking water.

Even where wastewater has undergone significant treatment, the irrigation area should always be managed according to the approved system requirements.

Children, pets and visitors should not interfere with wastewater irrigation equipment.

The irrigation area also needs to remain available for its intended purpose.

Poorly positioned surface irrigation can become inconvenient if the homeowner later wants to redesign gardens, construct buildings or change how that part of the property is used.

Advantages of Subsurface Wastewater Irrigation

The most obvious benefit of subsurface irrigation is appearance.

Because the irrigation lines are underground, there may be little visible evidence of the wastewater irrigation system once installation and landscaping are complete.

This can create a cleaner appearance around the home.

There are also no above-ground sprinklers in the irrigation zone to accidentally hit with the mower.

Another advantage is that treated wastewater is delivered into the soil rather than being sprayed above the ground surface.

For many homeowners, this makes subsurface irrigation attractive for residential properties where aesthetics and usability are important considerations.

However, it still needs to be carefully designed, installed and maintained.

Disadvantages of Subsurface Wastewater Irrigation

Because subsurface irrigation is underground, homeowners cannot simply look across the lawn and see whether every part of the irrigation network is working correctly.

Damage, blockages or poor distribution may not always be immediately visible.

Subsurface pipework can also potentially be affected by roots, excavation, landscaping, construction activity or vehicles if the irrigation area is not protected.

If someone purchases the property years later and does not know where the irrigation lines are located, they could accidentally damage them while installing a fence, planting trees, excavating a garden or completing other work.

Keeping accurate plans of the wastewater system is therefore extremely important.

Homeowners should know where the treatment tank, access points, pumps, pipework and irrigation areas are located.

Can You Plant Gardens Over Wastewater Irrigation Areas?

Landscaping around wastewater irrigation needs careful thought.

Vegetation can play an important role in helping manage moisture and nutrients within an irrigation area, but this does not mean every plant is appropriate.

Large trees with aggressive root systems can potentially interfere with underground irrigation lines.

Deep excavation for landscaping can also damage subsurface systems.

Homeowners should discuss proposed planting with their wastewater designer or service provider, particularly when substantial landscaping is planned.

As a general principle, the irrigation area should remain accessible and should not be altered in a way that interferes with its approved wastewater management function.

If you plan extensive gardens, retaining walls, sheds, pools or future building extensions, tell your wastewater designer before the system is installed.

Planning these features early can save considerable inconvenience later.

Can You Drive Over a Wastewater Irrigation Area?

Wastewater irrigation areas should generally be protected from vehicles and heavy machinery unless a system has been specifically designed and approved for those conditions.

Driving over irrigation lines can compact soil and potentially damage underground infrastructure.

Heavy vehicle traffic may be particularly problematic.

This is another reason wastewater design needs to be considered early when planning a new home.

Think about where vehicles will travel during construction and after the home is completed.

Consider:

• Driveways.
• Garages.
• Carports.
• Boat parking.
• Caravan storage.
• Delivery access.
• Future sheds.
• Turning areas.
• Access for maintenance vehicles.

If these areas are identified before the wastewater system is designed, the irrigation area can be located accordingly where site conditions allow.

How Much Irrigation Area Will You Need?

There is no single irrigation area size that suits every household.

The required land application area can depend on several factors, including wastewater volumes, the number of occupants, soil characteristics, treatment method, site constraints and local requirements.

A large household typically creates more wastewater than a smaller household.

However, household size is only part of the equation.

How the soil accepts and manages the treated wastewater can be equally important.

This is why simply asking, “How many square metres do I need?” without assessing the property may not provide a reliable answer.

A suitable wastewater assessment should determine the appropriate land application requirements for the particular site.

What Happens During Heavy Rain?

Rainfall is an important consideration for onsite wastewater management because wastewater continues to be produced inside the home even when the ground outside is wet.

A well-designed wastewater management system therefore needs to take local conditions into account.

Homeowners can also help by reducing unnecessary water use during prolonged periods of heavy rain.

Large amounts of household water entering the wastewater treatment system increase the amount that ultimately needs to be managed.

Fix leaking taps and toilets, spread laundry loads throughout the week and avoid unnecessary water use.

Stormwater must also be managed separately from the onsite wastewater system.

Roof water, driveway runoff and other stormwater should not be deliberately directed into wastewater treatment infrastructure.

Surface Irrigation Maintenance

Surface wastewater irrigation should be inspected regularly.

Homeowners should watch for signs such as:

• Damaged sprinklers.
• Uneven spray patterns.
• Blocked outlets.
• Broken pipes.
• Persistent wet areas.
• Unusual odours.
• Water flowing outside the approved irrigation area.
• Sprinklers that are no longer operating.
• Areas of unusually heavy vegetation growth.
• Damage caused by mowing or gardening.

If something appears abnormal, contact your wastewater service provider rather than simply disconnecting or relocating parts of the irrigation system.

The irrigation network was installed as part of the approved wastewater management design, so changes can affect system performance.

Subsurface Irrigation Maintenance

Subsurface irrigation also needs ongoing attention even though much of it is hidden.

Homeowners should watch for:

• Unexpected wet patches.
• Persistently soggy ground.
• Unusual odours.
• Areas where grass growth changes noticeably.
• Water surfacing from the ground.
• Pump alarms.
• Changes in wastewater system performance.
• Damage following excavation or landscaping.
• Problems after heavy vehicles have crossed the area.
• The absence of visible sprinklers does not mean the irrigation system is maintenance free.

Wastewater treatment systems contain pumps, controls and other components that require ongoing inspection and servicing.

Why Regular Wastewater Servicing Matters

An onsite wastewater treatment system is working every day.

Unlike a conventional sewer connection where wastewater leaves the property through a sewer network, an onsite system treats and manages wastewater on your land.

That makes maintenance especially important.

Regular servicing can identify problems before they become larger failures.

A service technician may inspect treatment components, pumps, alarms and other equipment according to the requirements of the particular system.

Homeowners should also pay attention to alarms or warning indicators.

Do not repeatedly silence a wastewater alarm without investigating why it has activated.

An alarm could indicate a pump, water level or treatment problem that needs attention.

Surface vs Subsurface Irrigation and Council Approval

For NSW homeowners, your local council plays an important role in onsite wastewater management.

Under NSW arrangements, councils regulate the installation and operation of onsite sewage management systems. For example, councils commonly require approval under Section 68 of the Local Government Act 1993 for onsite sewage management activities. Penrith City Council specifically states that council approval is required for installation or operation of onsite sewage management systems, while Clarence Valley Council requires a Section 68 onsite wastewater application when installing or upgrading a system.

Individual council policies and application requirements can vary.

That means homeowners should never assume that a wastewater design approved in one council area will automatically satisfy another.

Before buying a wastewater treatment system, determine what documentation your local council requires.

Depending on the project and council, this may include a wastewater report, site and soil assessment, proposed treatment system details, land application design, site plans and other supporting information.

Your wastewater consultant, plumber, installer or system supplier can help explain what information may be required, but final approval remains a matter for the relevant authority.

Should You Choose the Tank Before the Irrigation System?

Ideally, the wastewater treatment system and land application area should be planned together.

One mistake homeowners can make is purchasing a tank first and then trying to determine where the treated wastewater will go.

A better process is to understand the complete wastewater requirements of the property before making the final purchase.

Start with the site.

• Determine the wastewater load.
• Understand the soil.
• Identify the available irrigation area.
• Consider council requirements.

Then select an appropriate treatment system and irrigation method.

This reduces the risk of purchasing equipment that does not suit the approved wastewater design.

What Should You Ask Before Buying a Wastewater System?

When comparing wastewater systems, homeowners should ask more than simply, “How much does the tank cost?”

Ask:

• What wastewater treatment system is recommended for my property?
• Does my council accept this type of system?
• What irrigation method has been specified?
• Will I have surface or subsurface irrigation?
• How large is the land application area?
• Where will it be located?
• Can I landscape the area?
• Can vehicles travel over it?
• What areas must remain clear?
• What maintenance does the irrigation system require?
• How often does the treatment system need servicing?
• What happens if an irrigation line becomes blocked?
• Who services the system?
• Are replacement pumps and components readily available?
• What warranty applies?
• What documentation will I receive?
• Who provides the information required for council approval?
• What installation work is included?
• What is not included in the quoted price?

These questions can provide a much better understanding of the true cost and ongoing responsibility of owning an onsite wastewater system.

Planning for Future Property Improvements

Homeowners should think several years ahead when choosing the irrigation location.

You may not want a swimming pool today, but could you want one later?

What about:

• A granny flat?
• Large shed?
• Workshop?
• Additional driveway?
• Outdoor entertaining area?
• Caravan parking?
• Garden beds?
• Children’s play area?
• Home extension?
• Water tank?
• Detached garage?

If your wastewater irrigation area occupies the only suitable location for a future building, changing it later may involve additional wastewater assessment and infrastructure work.

Discuss your long term property plans during the original wastewater design process.

Even if those improvements never happen, preserving suitable areas can give you more flexibility.

What Happens When You Buy a Property With Existing Wastewater Irrigation?

If you are purchasing a rural or unsewered property with an existing wastewater treatment system, do not assume everything is working correctly simply because there is no obvious problem during the inspection.

Ask the seller for wastewater documentation.

Look for:

• Council approvals.
• Approval to operate documentation where applicable.
• Wastewater reports.
• System plans.
• Irrigation layouts.
• Installation details.
• Service records.
• Repair history.
• Manufacturer information.
• System model.
• Age of the system.
• Pump replacement records.

Knowing where the irrigation lines are located is particularly important for subsurface systems.

Some NSW councils require onsite sewage management systems to be registered and operated under council approval processes. Central Coast Council, for example, states that onsite sewage management systems must be registered and require an approval to operate.

Requirements can differ between councils, so buyers should contact the relevant local council when completing their due diligence.

Warning Signs Your Wastewater Irrigation May Have a Problem

Wastewater systems often provide clues when something is not operating correctly.

Contact a suitable wastewater professional if you notice:

• Persistent sewage or wastewater odours.
• Wet or boggy areas around irrigation lines.
• Water pooling on the surface.
• Wastewater escaping outside the designated irrigation area.
• A wastewater alarm that keeps activating.
• Sprinklers not working.
• Unusual sprinkler pressure.
• Very uneven irrigation.
• Surface water where a subsurface system is installed.
• Toilets or drains behaving unusually in combination with wastewater system alarms.
• Extremely lush growth concentrated in one small area.
• Visible pipe damage.
• Problems that appeared after excavation, landscaping or vehicle movement.

Early attention can prevent a relatively small issue becoming a major system failure.

Surface vs Subsurface Wastewater Irrigation: Which One Should You Choose?

For many homeowners, subsurface irrigation may initially sound more attractive because the irrigation infrastructure is hidden.

For others, the accessibility and simplicity of visible surface irrigation may be appealing.

However, the decision should not be based on appearance alone.

The correct wastewater irrigation method is the one that suits:

• Your soil.
• Your site.
• Your wastewater volumes.
• Your available land.
• Your landscaping.
• Your treatment system.
• Your local council requirements.
• Your future plans for the property.

Your wastewater designer should consider these factors when recommending a solution.

The Most Important Thing for Homeowners to Remember

Your wastewater tank and wastewater irrigation area are not two separate systems.

They are parts of the same onsite wastewater management process.

The treatment tank treats the wastewater.

The irrigation or land application system manages the treated wastewater after it leaves the treatment system.

Both need to work correctly.

Installing an excellent wastewater treatment system but poorly planning the irrigation area can create ongoing problems.

Likewise, a properly designed irrigation area cannot compensate for a wastewater treatment system that is not being maintained correctly.

The best results come from treating the entire wastewater system as one complete solution.

Talk to Eco Septic Before Choosing Your Wastewater System

If you are building, renovating, replacing an old septic system or purchasing a property that requires onsite wastewater treatment, understanding your irrigation requirements early can make the entire process easier.

At Eco Septic, we understand that every property is different.

Before deciding between surface and subsurface wastewater irrigation, make sure you understand the wastewater report, site requirements, council requirements and the type of treatment system being proposed.

If you already have a wastewater report, having it available when requesting a quote can help determine which wastewater system and accessories may be appropriate for your project.

If you are still at the early planning stage, speak with the relevant wastewater professionals and your local council about the information required for your property.

Planning the treatment system and irrigation area correctly from the beginning can help create a wastewater solution that works effectively with your home, land and future plans.