The online application form concerned is a matter for Irish Water in the first instance. Irish Water has established a dedicated team to deal with representations and queries from public representatives. They may be contacted via email at oireachtasmembers@water.ie or by telephone on 1890 278 278.
However, clarification was sought from Irish Water and I have been informed that the online application is designed to accept the details for up to 10 occupants at the same address. The householder is required to scroll down to see the extra fields as this cannot be accommodated within the same screen view.
Any household with occupancy in excess of 10 is being asked to apply to Irish Water by phone so that the exact details can be captured for the household in question.