Domestic Waste Water from Single Houses

There are an estimated 500,000 domestic waste water treatment systems (DWWTS) (i.e., septic tanks  and treatment systems) systems in Ireland treating waste water from single houses i.e. houses not connected to a public sewer system. DWWTS accept waste water from toilets, showers, sinks, wash hand basins, washing machines and dishwashers. The greater the population of the dwelling, the greater the volume of waste water produced. A DWWTS is assumed to have a daily hydraulic loading for each person of 150 litres and typical household occupancy of 2.8 people.  On a national scale, this equates to a liquid discharge of 210,000 m3 per day or 46 million gallons (equivalent to 84 Olympic swimming pools). There are a number of different pollutants in domestic waste water, each of which can cause problems for health and the environment. 

On-site DWWTS can threaten public health and water quality when they fail to operate satisfactorily. When the wastewater is not absorbed by the soil it can form stagnant pools on the ground surface. In such failures, humans can come in contact with the wastewater and be exposed to pathogens, e.g. faecal coliforms (see Table below). Foul odours can also be generated. Typically there are approximately 1 million E. coli bacteria in one litre of effluent from a septic tank serving a normal household. The drinking water standard for E. coli and coliform bacteria is zero.

PollutantSeptic Tank SystemProprietary Systems
Faecal Coliforms  >1million/100ml  >5-10,000/100ml
Nitrogen mg/l N  50  30
Phosphorous mg/l P  10  10
 BOD mg/l  200  20

Did you know that maintaining your domestic waste water treatment system helps protects you and your neighbour’s private wells?

Did you know that you should have your domestic waste water treatment system inspected and de-sludged on a regular basis?

Do you know as a homeowner you are responsible under the Water Services Act (as amended) for maintaining your domestic waste water treatment system?

If properly designed, installed and maintained, your DWWTS (including septic tanks) can provide long term, effective treatment of domestic wastewater

View details on Code of Practice for Waste Water Treatment Systems for Single houses.

If you do not maintain your system it may be necessary to replace it, which may cost a lot of money.  A malfunctioning system can contaminate groundwater and therefore private wells. It may also result in ponding of effluent, which will pose a risk of disease to children and form odours.

Owners of DWWTS are required to operate and maintain their systems so that they do not pose a risk to human health or the environment.  New legislation was introduced in 2012 outlining the responsibilities of system owners. 

Learn More

Information on the legislation  

Animation on how a DWWTS (septic tank or treatment system) works

What to expect from an Inspection

There are certain things you can do to make sure that your DWWTS (septic tank or treatment system) is working properly - See what you can do.

If you are concerned about your private well - read leaflet on 'Is Your Well At Risk from Your Septic Tank'.

If you have more questions on your DWWTS (septic tank or treatment system) -   see our Frequently Asked Questions (FAQs) section

The EPA has published guidance on wastewater treatment and disposal systems for single houses which should be consulted when installing new DWWTS (septic tanks or treatment systems).

If you fail an inspection under the Water Services (Amendment) Act 2012 you will have to take steps to repair or remediate your DWWTS so that it does not cause a risk to human health or the environment.  Advice notes on remediation and replacement of DWWTS.