No, Uisce Éireann does not generally allow permanent structures over public water mains, since the pipe must stay accessible for repair and maintenance. If a main crosses a development site, it will usually need to be diverted or a protective wayleave zone left clear, and this should be checked before you finalise a design.
Public water mains are owned and operated by Uisce Éireann, and as with sewers, the company's standard position is that permanent structures should not be built directly over a main, because the pipe needs to remain accessible for leak repair, valve maintenance and eventual replacement. Where a water main is found to run through or beside a proposed development site, Uisce Éireann will typically require either a diversion of the main around the building footprint, paid for by the developer, or a protected wayleave corridor kept free of structures, walls, or in some cases even significant tree planting, above and around the pipe.
The width of the protected zone and whether a diversion is mandatory depends on the size and depth of the main, ground conditions and the type of structure proposed; larger trunk mains serving whole areas are treated more strictly than small distribution pipes serving individual properties. For single houses, it is common for a service connection pipe to run under a driveway or garden, which is manageable, but a trunk main crossing a site can materially affect where a house can be positioned and should be identified at an early design stage.
You should request mapping of water mains and their approximate location from Uisce Éireann, or through a pre-connection enquiry, before committing to a site layout, and where there is uncertainty, arrange for the main to be physically located (for example by trial hole) since as-built records are not always fully accurate.