The Ultimate Guide to Septic Tanks: Ireland Edition

We have put together a comprehensive guide detailing everything you need to know when installing and maintaining a septic tank and percolation area in Ireland.

What is a septic tank?

A septic tank is an underground container that collects wastewater generated in your home or commercial facility. Using natural processes a septic tank removes suspended solids from the wastewater, this is considered “primary wastewater treatment”.

As there is limited anaerobic digestion (a process by which microorganisms break down organic matter in the absence of oxygen) the majority of the “secondary wastewater treatment” is carried out in a percolation area (a network of sub-surface perforated pipes in stone-filled trenches through which the final wastewater is distributed into the soil where it receives further treatment).

How does it work?

• Wastewater (toilets, showers, baths, sinks, washing machines, dishwashers) from your home or commercial facility flows by gravity into the septic tank through an inlet pipe.

• Heavy solids sink to the bottom of the tank while oils, fats, and greases create a scum layer on top, the remaining “effluent” is where the anaerobic digestion takes place.

• The effluent leaves the tank through an outlet pipe and flows by gravity to your percolation area. An organic layer (biomat) forms between the base of the stone-filled trenches and subsoil which allows more time for the remaining pathogens to be removed before the treated effluent discharges to groundwater.

• The remaining solids, oils, fats, and greases are removed periodically by a licensed de-sludging company that will safely dispose of the waste from your tank.

Why do I need one?

If you are building/renovating in a geographical area that does not typically have access to the main sewer you will need to install some sort of on-site wastewater treatment system to safely treat and dispose of your wastewater.

Untreated wastewater can contaminate local water supplies with harmful bacteria and viruses, it can also cause pollution of the environment through excessive phosphorus and nitrogen production.

How do I know if my site is suitable?

When you are building/renovating a new/existing home or commercial facility you will need to have an EPA Site Suitability Assessment carried out as part of your planning application. This will determine if you have suitable ground conditions and space available on-site to install a septic tank and percolation area.

For example, a 4 bedroom house requires a tank with a capacity for 6 people, you would need 6 trenches 18 metres long with 2.5 metre centres (each trench is 500mm in width) which would be a total area of 270m2 to safely treat and dispose of your wastewater.

You also need to meet the minimum separation distances from the water table or bedrock on-site as well as the property itself, surrounding boundaries, wells, other dwellings, public roads, etc. If you are not able to meet the separation distances you will need to install a packaged secondary wastewater treatment system which requires less space on-site and gives you more flexibility when it comes to ground conditions.

If a site is deemed unsuitable for discharging treated effluent to groundwater, alternative options, if any, will need to be discussed with the local authority.

Where can I find the septic tank regulations in Ireland?

If you would like to learn more about septic tank regulations in Ireland we recommend you check out the EPA Code Of Practice 2021, S.R. 66:2015, and the Building Regulations Technical Guidance Document H.

Do septic tanks need to be certified to be sold in Ireland?

Yes, septic tanks in Ireland need to be tested and certified in accordance with S.R. 66:2015 and EN 12566 Part 1. You can view the full list of domestic on-site wastewater treatment systems (including septic tanks) that are currently certified to be sold in Ireland here.

How much does it cost to install a septic tank and percolation area?

We estimate a septic tank and percolation area installation will cost anything from €3,000 to €5,000 depending on the contractor you choose and the location of the proposed site.

Do I need to register my septic tank?

Yes, domestic on-site wastewater treatment systems (including septic tanks) need to be registered, you can do so here.

Am I eligible for a grant to repair or replace my septic tank?

There are grants of 85% up to a maximum of €5,000 available under the following schemes:

National Inspection Plan: If your on-site wastewater treatment system (including septic tanks) is inspected by the local authority and they find an issue with your system you will receive an advisory notice within 21 days of inspection. You can then submit an application to the relevant local authority to avail of the grant scheme under the national inspection plan.

High-Status Objective Catchment Areas: If you would like to check if you are in a high-status objective catchment area you can enter your EIRCODE here. If you are eligible you can then submit an application to the relevant local authority to avail of the grant scheme under high-status objective catchment areas.

Priority Areas For Action: These areas will be identified by the local authority waters programme office, if you are eligible you will receive confirmation in writing, you can then submit an application to the relevant local authority to avail of the grant scheme under priority areas for action.

Please note that routine maintenance and or de-sludging is not covered under the grant scheme, this is an essential part of owning and operating an on-site wastewater treatment system.

For more information click here.

Will my septic tank be inspected?

Yes, your on-site wastewater treatment system (including septic tanks) can be inspected by the local authority. You will receive at least 10 working days notice prior to an inspection being carried out by an EPA (Environmental Protection Agency) appointed inspector.

If your on-site wastewater treatment system is fully operational you will receive a certificate to prove it. If the inspector finds an issue with your system, you will receive an advisory notice within 21 days of the inspection. This notice will outline the problems with your on-site wastewater treatment system and give you a certain amount of time to fix them. You may be able to get a grant to repair or upgrade your system, for more information click here.

How often do I need to get my septic tank emptied?

Your on-site wastewater treatment system (including septic tanks) will need to be de-sludged at regular intervals. This will depend on the type of on-site wastewater treatment system you have installed as well as the hydraulic and/or organic loading/capacity.

As a rule of thumb, we recommend that most of our customers will need to de-sludge their on-site wastewater treatment system every 12-18 months.

How much does it cost to empty my septic tank?

The cost to empty a septic tank in Ireland can vary depending on the location and size of the tank. It generally ranges between €250 to €450. However, it is recommended to get a quote from a licenced de-sludging company for a more accurate cost.

What should I do if my septic tank has flooded?

We recommend using toilets, showers, baths, sinks, washing machines, and dishwashers as little as possible until you can resolve the issue. You may need to have your septic tank de-sludged to prevent any risk to human health/contamination of your drinking water and/or the environment. If you are constantly having issues with your on-site wastewater treatment system (including septic tanks) we recommend consulting an engineer or suitability qualified wastewater professional to resolve the issues permanently.

Where can I find a licensed company to empty my septic tank?

Unfortunately, we don't provide this service but we have put together a list of licensed de-sludging companies throughout Ireland. Check out the full list here.

What are septic tank additives?

Septic tank additives are products that are added to a septic tank to enhance the performance of the system. They are typically microorganisms or enzymes that are designed to break down the waste in the tank and help prevent blockages and flooding.

These additives can help reduce the frequency of de-sludging and maintenance needed for the septic tank. Some common types of septic tank additives include bacteria, enzymes, and chemicals that break down solids and scum.

It is worth noting that not all septic tank additives are beneficial and some can even be harmful to the system. It's important to research and choose the right product and use it according to the instructions. Also, it's important to note that even with the use of additives, regular maintenance such as de-sludging and inspections are still necessary.

Do I need to use chemicals or additives in my septic tank?

This is a question our customers ask us regularly, the answer is no, a septic tank that is operating correctly does not require any additional chemicals or additives.

What are the most common issues with existing septic tanks?

The most common issues our customers face with existing septic tanks are:

The site isn’t suitable: Unfortunately, some on-site wastewater treatment systems (including septic tanks) have been specified and installed incorrectly over the years. This can be for various reasons such as excessive organic/hydraulic loading, poor ground conditions, or limited space available on-site causing problems with separation distances from the property itself, bedrock and/or a water table, surrounding boundaries, public roads, wells, and other dwellings which potentially causes a risk to human health/contamination of our drinking water and the environment.

Improper maintenance: If a septic tank hasn’t been maintained properly it can cause major issues with your percolation area. Over time, solids from your septic tank system can flow out of the tank and into the percolation area if they are not removed periodically. This causes the ground to become saturated (blocked) which prevents the treated effluent from returning safely to groundwater. The untreated wastewater will eventually saturate your garden which causes a huge risk to human health/contamination of the environment.

Structural damage: If your septic tank is damaged or if you have pipework leaking you could potentially be contaminating the environment and saturating the soil.

Another common way damage causes an issue is by allowing natural groundwater to enter your septic tank. Your septic tank was never designed to deal with rainwater/groundwater which can cause your septic tank to flood and allow solids to enter your percolation area.

Over time, this causes the ground to become saturated (blocked) which prevents the treated effluent from returning safely to groundwater. The untreated wastewater will eventually saturate your garden which causes a huge risk to human health/contamination of the environment.

If you think you might be experiencing these issues we recommend scheduling a septic tank inspection with a wastewater professional to diagnose your ongoing issues and provide a detailed roadmap to achieving a long-term solution once and for all.