The Tánaiste Joan Burton says the amount of data Irish Water is getting from PPS numbers is limited.
Ms Burton has warned that any abuse of the numbers is protected as a criminal offence and under data protection legislation.
Concern has been expressed by many people in giving PPS numbers to Irish Water - the utility says it needs them to allocate allowances.
The Tánaiste says the data being collected by Irish Water is not extensive and is limited to two questions.
She said: "One is 'Is this a valid PPS number?' Yes or no, is it a real PPS number? And the second question is simply 'Is the person to whom this PPS number is assigned, is that person under 18?'
"There is no other data exchange involved."