Private Water Supplies - Case Study 2011/05

Best practice in relation to co-regulation of drinking water safety at premises by water companies and local authorities

This case study relates to an estate serving approximately 30 consumers in a mixture of domestic and commercial premises including owner-occupied and rented property, offices and two food premises. The estate was included in the local water company’s compliance monitoring programme because some of the premises appeared on the company’s billing record. A random tap sample collected by the water company was positive for all faecal indicator organisms (E.coli and coliforms). The onsite chlorine measurement associated with this sample was very low (0.1 mg/l) and not as expected for the local mains water supply (0.59mg/l recorded in a nearby village).

The water company issued boil water advice to all the consumers on the estate and contacted the local authority because the investigation had identified that the premises sampled was not a customer. The local authority informed the water company that historically a private water supply had served the estate and was able to provide details of properties on the supply from archived records. The water company had taken wider investigational samples from the estate, a neighbouring village and the upstream mains water supply, including the service reservoir and treatment works. All these samples gave satisfactory results except for the repeat sample from the original premises which was positive again for E.coli, Enterococci and Clostridium perfringens. By this time, residents of one of the domestic dwellings had reported that the whole family had recently suffered from gastroenteritis. To safeguard the wider public supply, the water company installed a double check value at the point where mains water entered the estate and commenced fittings inspections at all of the premises.

Installation of check valve

Installation of check valve

A review of meter readings for the mains water supply into the estate showed that the average monthly volume of water used had dropped by 92% over the last five years suggesting an alternate water source. When the mains supply to a number of dwellings was shut off, water was still available in the property. Further investigations uncovered an open valve on the private water supply proving it had not been abandoned, but was in fact supplying some of the properties and presenting a risk of contamination by means of the cross connection. The private water supply was of a higher pressure than the mains supply therefore contaminated water was being drawn into wider network. In total, the fittings inspections identified 44 non-compliant plumbing systems on the estate and the estate was served with a remedial water fittings regulations Notice by the water company.

Based on the technical investigation and information provided by the water company, the local authority concluded that the private supply was posing a potential danger to human health, and served a Regulation 18 Notice, setting out two options for remediating the supply:

Permanent disconnection of the private water supply at the source by cutting and capping the out-flow pipes and identification and permanent disconnection of all cross-connections with the mains supply. When complete, disinfection and flushing of all distribution pipes.

As an alternative to permanent disconnection of the private supply source, installation of appropriate treatment and disinfection and removal of the connection.

Private supply storage tank now disconnected from the system

The Notice set out further conditions requiring use of only approved products and chemicals (Regulation 5), and notification of consumers in advance of any supply interruptions linked to planned works with provision of an alternative supply. There was no appeal to the Notice and the estate decided to disconnect the private water supply. The water company and local authority jointly inspected and verified the disconnection works and the supply to this estate is now reported as a private distribution system.

This case study illustrates effective co-regulation by the local authority and the water company in relation to the powers and duties of each as set out in the Private Water Supplies Regulations and the Water Fittings Regulations (1999) respectively. The water company’s role is to inspect and ensure compliance with the Fittings Regulations and the local authority’s role is to require remedial works to improve any private supply and to secure its ongoing safe management and maintenance. The common duties are communication with each other and with consumers.