A strike by up to 2,000 Water Service workers in the North could cause disruption to water supplies and a risk of environmental pollution, the British government has warned.
Workers are staging a one day strike at the start of ongoing industrial action in opposition to the government's planned water reforms which unions say could result in up to 700 job losses.
Amid mounting opposition to the water service reforms, public rallies organised by the unions and organisations against the introduction of water rates are being staged in Belfast and Derry on Saturday.
The Department of Regional Development has pledged the Water Service is taking every reasonable precaution to provide essential normal water and sewerage services today.
But a spokesman said: "This is an almost unprecedented situation, with the possibility of some disruption to water supplies and the risk of environmental pollution."
The Water Service said it was implementing established contingency plans for dealing with major incidents.
It had been liaising with the other emergency services - including the Fire Service, police and heath authorities - to safeguard public health, protect the environment and "maintain essential support to normal daily life in Northern Ireland," said the spokesman.
The co-operation of the community would be a vital assistance in ensuring any service disruption was remedied as quickly as possible, he added.
The Water Service Unions - AMICUS, ATGWU, GMB and NIPSA - said the one day strike was the start of industrial action which would also involve a work to rule and withdrawal of goodwill.