NI Water have hit out after four tonnes of rubble had to be removed from a Co Antrim drain,
The company said the Aghalee sewer was probably blocked by building waste "irresponsibly" put down a manhole.
The agency said it's increasingly removing "extensive piles of rubble" from our pipes, including stones from a sewer in Stewartstown Road, West Belfast, which took days to extricate and disrupted traffic.
Denis McCavigan, Wastewater Manager, said: "Staff working on the blockage could not believe the sheer amount of stones, they took days to remove, not to mention the cost.
"Rogue discharges like this are commonly found around building sites where the remains of concrete are washed down into the drainage system.
"This is typical of material getting into our sewers from new building works and developments. Combined with bricks, stones and inappropriate rags, they can become a real pain to remove and a very expensive piece of maintenance work.
Mr McCavigan said opening a manhole to get rid of waste was prohibited, and could cause sewers to flood into streets and rivers.
He added: "This act shows not only lack of respect for our network but also for the people living in the area. NI Water would remind all customers that opening a manhole to discharge any material or washing substances into the drainage system is prohibited.
"By doing this, you are obstructing a working sewer which is only designed to take wastewater away from homes and businesses.
"By obstructing the sewer in this way, it reduces the pipe capacity and the volume of wastewater it is able to take; this can lead to increased blockages and out of sewer flooding in the street or into a river. Out of sewer flooding is extremely unpleasant and affects the whole community and damages the environment.
"We have all seen the disgusting effects of an overflowing manhole in the street and no one wants to see or smell it but the reality is, it happens regularly at a cost of millions to NI Water each year."
Last year a 30 foot concrete-berg, big enough to build a garden wall, was pulled from a drain in Omagh.
He added: " In the last ten years, NI Water has spent over £1 billion investing in water and wastewater infrastructure but no amount of investment will completely stop blocked pipes if people continue to misuse the sewerage system."
niwater.com
