Bosses were also warned of problems for meterless households in scheme to target 58,000 consumers
Irish Water's plans to charge 58,000 households for excessive usage were delayed over data protection concerns, it has emerged.
There were also concerns over how to deal with those households that have no water meters.
Letters and information packs were being prepared for dispatch last October, telling households what they could do to reduce their water consumption and how Irish Water could help.
But the plan was postponed to deal with issues around how customer data would be managed, unmetered houses, and building IT infrastructure to support the project.
Internal records obtained under freedom of information laws describe detailed discussions to ensure that plans to start charging for excessive usage would be "very carefully managed".
There would need to be messaging around how Irish Water was going to manage households with no meters - and how excessive use for them would be calculated.
Discussions are now going on with the Data Protection Commissioner over how the volume of personal data involved in the proposals can be properly managed.
This would include names, addresses, water usage, the number of people living in each house, and special medical requirements of residents who might require additional water use.
It also includes strong indicators of when people are likely to be home based on when water is being used on a day-to-day basis, which in the event of a computer breach could create a burglary risk for households.
A spokeswoman for Irish Water said that household water conservation was a "unique project" and that the Department of Housing were currently consulting with the Data Protection Commissioner on the matter.
She said: "[We have] taken all the necessary steps to try to ensure that our approach is in line with GDPR requirements and that all measures are taken to protect personal data."
The spokeswoman said that while GDPR was a key issue, detailed work on customer communications, building IT systems to ensure accurate notification, and identifying unmetered households were also "essential to the progression of the project".
"All of these elements are reaching a state of readiness. The project cannot proceed unless and until all elements are ready," she said.
The Irish Water records explain how the process for charging would happen with a 'call to action' letter and leaflet sent to households at first.
This would include a step-by-step guide on what a customer in receipt of a letter should do next - "what options are open to them, what help can Irish Water provide, what can the household do?"
Customers would be told how much water they had used in the preceding 12 months and that this was "above the excess threshold amount".
The letter would say: "If you continue to use more than 213,000 litres a year, you may have to pay excessive usage charges for water used above this amount."
Officials from the Department of Housing also warned Irish Water that they must stick rigidly to what was allowed for in legislation in their letters to households.
"If they appear to suggest that Irish Water is operating differently to what is in the legislation, they will be open to challenge," said one email.
The excess would be charged at the rate of €1.85 per 1,000 litres up to a capped amount of €250. Customers with water in and water out services would be capped at €500 per a year.
The process would target 6,000 people with the highest excess use first.