President Michael D Higgins has signed into law the Water Services Bill 2014.
The legislation deals with many of the changes announced by the Government in November in relation to water charges - including a reduction in the bills households will face.
The Government's revised legislation passed through its final stages in the Seanad just before Christmas.
The discussions failed to result in any amendments being passed.
A number of Oireachtas members had asked Mr Higgins not to sign the bill into law and instead refer it to the Council of State.
A statement today said careful consideration had been given to all aspects of the Bill and the submissions Mr Higgins had received.
A small number of protesters staged a short protest outside Áras an Uachtaráin after President Higgins signed the bill into law.