The Isle of Man Water Supply Byelaws 2002 (the Byelaws) are intended to prevent the waste, misuse, undue consumption or contamination of public water supplies. All who install or use plumbing systems have a legal duty to comply with these Byelaws.

As owners and occupiers of port premises, the port authorities have legal duties to their employees and to those who visit their ports. Under the Water Act 1991 and the Byelaws they must ensure that water supplies within the Island's ports are adequately safeguarded against contamination. They must also take responsibility for ensuring that water fittings are installed and maintained in compliance with the Byelaws. Under health and safety legislation they must ensure their premises are not the source of a health and safety risk. Any serious risk to health from the water supplies may result in the supply being disconnected. We have the power to prosecute infringements of the Byelaws and are likely to recover the significant costs incurred in responding to a water contamination incident.

We have a duty to ensure that the water we provide to premises for domestic purposes (for example, drinking, washing and cooking) is 'wholesome' at the time it's supplied. Wholesome water complies with the water quality requirements in the Water Act 1991. After it has been supplied, water can become contaminated by being in contact with unsuitable materials in the plumbing system, by ingress of contaminants – for example into an uncovered storage cistern – or by backflow of contaminated water from fittings or appliances.

This guidance includes recommendations to assist port authorities in complying with their legal obligations and ensuring the safety of drinking water supplies in ports and their surroundings.