More than half of businesses will see their cost of water increase from today, as a result of changes to the charging system.
The balance of customers will see the amount they have to pay fall because of the alterations.
Irish Water says the vast majority of customers will see either a decrease or an increase of less than €250 per annum in their annual bills.
For those who will face larger increases, the utility says it put in place a number of support measures.
The introduction of the new standardised nationwide charging regime was due to go live on May 1 of last year.
But it was delayed twice by the Commission for Regulation of Utilities because of the pandemic and the pressure it was already putting on firms.
The new non-domestic tariff framework will impact over 164,000 businesses, farms, charities, public bodies, social enterprises and other non-domestic customers.
"The new tariff framework announced by our economic regulator, the Commission for Regulation of Utilities goes live on the 1st of October and will provide certainty for businesses and their representative groups," said Irish Water's Head of Customer Operations, Yvonne Harris.
"Irish Water understands the continued challenges faced by businesses; our aim is to ensure that every business across the country is provided with a clear, transparent, equitable charging regime regardless of location."
The new charging scheme will replace over 500 different tariffs across 44 separate areas, where customers previously paid different amounts depending on what local authority area they were operating in.
The new system will introduce four bands based on the level of consumption of the customer.
Irish Water has pointed out that there has been no change to the charges since 2014, or longer in many cases.
"The new framework will now standardise charges across the country while recovering the cost of providing water and wastewater services to non-domestic customers," said Ms Harris.
"Connections that see an increase of €250 or more will be transitioned to the new tariffs over three years.
"For connections that will face an increase of €750 or more, we will automatically apply a 10% cap to their annual bill increase in any one year."