Payments to Irish Water dropped by more than €9m in the utility's last billing cycle.
The drop in revenue collected at the end of March represented a reduction of 20pc when compared to the third quarter of last year.
The company has revealed 8,000 of the 200,000 customers who had signed up to pay their water charges by direct debit cancelled payments.
Irish Water has begun sending out its final round of bills, which are for the first three months of this year.
However, it is likely there will be another significant drop in payments. Following the General Election, there was speculation that the charges were to be shelved from March.
The Irish Water figures suggest that as the result of the General Election became clear many households decided not to pay any more water bills.
The last round of bills were sent in January and February. In total, €33m was paid to Irish Water in the fourth bill cycle of last year, compared to €42.3m in the third cycle.
Irish Water said while some customers began paying for the first time during the fourth bill cycle, others who paid earlier bills may not yet have paid their fourth bill, "which explains the fall in revenue".
Last year, 975,000 people paid at least one of their water bills, which represents around 64pc of those liable to pay.
However, Irish Water declined to release details for the percentage of customers who are fully paid up to date.
The amount collected over 2015 was €144m, which was 53pc of the total income due from domestic charges in the year.
"Payments received through all payment channels reduced during the month of March," the company said in a statement.
"Legislation suspending water charges is due before the Dail in June. Once this legislation is passed, we will update our customers," it added.
Sinn Fein water spokesman, Eoin O Broin said figures he obtained through a Freedom of Information request also revealed a "dramatic drop" in the number of people paying charges.
He said those figures show 36pc of people haven't paid any of their water charges over the last 12 months and that Irish Water failed to collect almost 50pc of their projected income from the charge.
"Unfortunately, Irish Water have not provided clarity on the number of customers who paid their water charges during the fourth billing cycle," he said.
"Instead, they provided cumulative figures. This is an attempt to hide the drop in the number of people who have stopped paying the controversial charge," he added.