Irish houses use two separate drainage systems: foul drainage carries wastewater from toilets, sinks and appliances to a public sewer or an on-site treatment system, while surface water drainage carries rainwater from roofs and paving to a soakaway, watercourse or surface water sewer. Technical Guidance Document H sets out how both are to be designed.
Drainage from a dwelling is separated at source. Foul water from sanitary fittings runs through pipework and inspection chambers to either a public foul sewer operated by Uisce Éireann or, in unsewered areas, to an on-site wastewater treatment system with a percolation area. Surface water from roofs, driveways and paved areas is collected separately and disposed of to ground, to a watercourse or to a surface water sewer.
Part H of the building regulations, with its Technical Guidance Document, covers pipe sizing, gradients, ventilation of the system, access for maintenance, and the requirement that drainage be adequate and not create a health risk. Local authorities may also apply their own drainage standards through planning conditions, particularly for surface water attenuation.