The minimum number of bills that the operator must issue in a year varies according to the average consumption recorded over the last three years (art.38 RQSII, 655/2015/R/IDR):

• 2 bills per year, on a semi-annual basis, for average annual consumption up to 100 cubic meters; 
• 3 bills per year, on a four-monthly basis, for average annual consumption from 101 to 1000 cubic meters; 
• 4 bills per year, every three months, for average annual consumption from 1001 m3 to 3000 m3; 
• 6 bills per year, every two months, for average annual consumption of more than 3000 cu m.