Hundreds of homeowners could be left facing huge bills because of problems over who is liable for upgrading their sewerage systems.
More than 600 properties at 21 sites across Northern Ireland have unadopted sewers. As it stands, there is insufficient or no funds in place to cover the cost of repairs.
A £2.3m shortfall exists, with officials warning responsibility could ultimately lie with individual homeowners.
The Department for Regional Development (DRD) said it was an "ongoing issue". It has undertaken a review into the matter.
Sewers and lateral drains connected to the public network used to be the responsibility of the property owner. Most are now maintained by Northern Ireland Water.
In the case of private or unadopted sewers, individual homeowners may be responsible for their maintenance. Documents presented to the Assembly's regional development committee provide an insight into the extent of the problem.
Some 21 sites have been identified where there is insufficient or no bond in place to cover the cost of remedial repairs.
The estimated value of these repairs is around £2.7m, with just £421,000 of bond cover in place - leaving a shortfall of £2.3m.
The affected sites, comprising more than 600 homes, are located across eight of the 11 new council districts. These include:
DRD has refused to disclose the exact locations, citing "commercial sensitivities". It could not confirm that each affected householder was aware that their property may be affected.
Ukip MLA David McNarry, who sits on the Assembly's regional development committee, said officials needed to be more open.
"DRD and NI Water are suppressing from these homeowners the extent of the problems," he said. DRD said that where the bond is insufficient to cover the cost of remedial works to bring the sewers to an adoptable standard, NI Water is currently unable to carry out the upgrade works.
This is because the company is not financed to carry a contingency fund to cover such works.
In documents seen by this newspaper, it states: "The responsibility rests with the developer's successors/assignees and responsibility may ultimately remain with those who are connected to the private unadopted sewerage system."
Mr McNarry said the value of affected homes could suffer. "Whatever the causes, the owners who purchased their homes in good faith are not at fault and should not be penalised," he added.
DRD was asked to detail which sites were affected.
A spokesperson said the department could not release this information "as it has commercial sensitivities attached to it".
Asked if each homeowner had been made aware that they could be liable, the spokesperson added: "NI Water has informed the department that it is in frequent contact with residents, residents groups or public representatives in the developments."