The utility company has emphasised that these sites, which include treatment works, pumping stations, and reservoirs, are not playgrounds and are operational 24/7.

NI Water said that while it doesn't want to discourage outdoor activities, there are hidden dangers that everyone needs to be aware of and people need to act responsibly to keep children and pets safe.

Francis Bradley, water supply manager with NI Water in the west, explained: "We traditionally see a huge increase in footfall across our property and sites at this time of year, especially over school holiday period. While its important and healthy to enjoy our beautiful countryside it is also vital to keep yourself and others safe by being aware of the often unseen dangers.

"Taking a nice walk on the crisp, cold day can be really refreshing but there can be risks in winter, particularly if temperatures dip and the water freezes over. Children or pets can be tempted to play on frozen watercourses, and adults can find themselves at risk if attempting to save them.

"We are reminding adults to act responsibility around watercourses and asking parents to keep their children safe. Stay a safe distance from water edges because accidents can happen and without extra care you could slip and fall in. Dog owners also need to remember to keep four legged friends on a lead if they are being walked near reservoirs and other bodies of open water."

Francis also advises many of NI Water's sites are in vulnerable remote locations: "Many of our sites are some distance from towns, villages and main roads, and often have poor mobile phone reception due to their location. This remoteness could hamper or delay rescue attempts if anyone gets into trouble – if there is any severe winter weather, those delays could be even longer.

''As winter continues, with cold, dark nights and long Christmas holidays, it is very important that everyone takes heed of the warnings and stays safe around NI Water sites.  It could be a very 'blue' Christmas indeed if you get into trouble. Don't take the risk; play safe and stay safe throughout the holiday period.''

NI Water is also appealing for public support in tackling anti-social behaviour at its sites.

Francis said: "Damage to our sites can affect the services we provide, including delivering fresh drinking water to our customers. The public are often our eyes and ears so we would like to ask for their support in reporting any anti-social behaviour, vandalism or criminal damage they see at any of our sites by contacting the police or phoning NI Water on 03457 44 00 88."

NI Water top five tips on playing safe and stay safe at its sites:

1.Don't climb on barriers and fences - They are there to protect you from serious injury and accidents when NI Water construction work is going on

2.Stay away from trenches and open manholes - They are dirty, deep and dangerous. They may also contain hazardous gases

3.Be careful near roads - never run out from behind parked vans or lorries as you could be knocked down and injured

4.Keep clear of equipment - You may see diggers, lorries, pipes and other equipment, but don't be tempted - steer clear and don't touch!

5.Obey 'Danger' signs - reservoirs and treatment works can be very dangerous places, so stay well away and always obey the warning signs