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Drinking Water Quality in Scotland 2002
Annex C Selected Drinking Water Quality Incidents
On 1 April 2002 Scottish Water inherited the drinking water infrastructure of Scotland from the three former water authorities, namely East of Scotland Water, West of Scotland Water and North of Scotland Water. Within 16 days of their inheritance, they had to deal with a drinking water quality incident in the area of North Ayrshire, which resulted in the distribution of bottled water and alternative supplies. Details of this incident as well as selected others, which occurred during 2002 are detailed below. There were a total of 27 Incidents reported during 2002, 15 of which resulted in bottled water and/or a boil notice being issued. Each local authority page in chapter 4 provides information in respect of those not highlighted below:
North Ayrshire April 2002:
This incident commenced on 16 April, when Scottish Water began receiving complaints of dirty water at a rate of 50 per hour from residents of North Ayrshire. It was suspected that the dirty water was due to manganese in the water mains and samples were taken. The initial samples gave results of 400-500 microgrammes per litre. The maximum concentration prescribed in the relevant Regulations is 50 microgrammes. The Consultant in Public Health Medicine instructed Scottish Water to issue advice to customers not to drink the water. Scottish Water prepared a notice to this effect and arranged alternative supplies. This involved placing static tanks on street corners and providing supplies of bottled water to special needs customers. The area affected by this incident included West Kilbride, Ardrossan, Saltcoats and Dalry. In total, approximately 37,000 customers (15,000 properties) were affected. The maximum levels of total manganese recorded in the samples taken during the incident ranged from 1,190 microgramme per litre in West Kilbride to 463 microgramme per litre in Saltcoats. Following remedial works and the gentle flushing of the affected water mains supplies were returned to normal by 19 April.
Following consideration of the initial complaints the Drinking Water Quality Regulator for Scotland (DWQR) decided that a full investigation was required and requested details from Scottish Water of the first 50 customer complaints it had received. The DWQR issued questionnaires to these 50 people. Thirty-three responses were received to the questionnaire and witness statements were taken from 7 of the respondents. Considerable disruption and concern was created by Scottish Water and, from the witness statements and analytical data, it was considered that Scottish Water had committed the offence of supplying water unfit for human consumption contrary to section 76C of the Water (Scotland) Act 1980. It was therefore determined that a report should be submitted to the Procurator Fiscal.
Following consideration of the report, the Procurator Fiscal (PF) decided to take no further action in relation to the report submitted to him. In reaching this decision, the PF took into account the work that had been carried out by Scottish Water in the interim period to minimise the risk of such an accident recurring.
Glasgow August 2002:
An extreme rainfall event took place on 31 July, which seriously challenged the water treatment process at a number of water treatment works across Scotland. One of the works affected was Milngavie water treatment works in Glasgow. This works received contaminated water from Loch Katrine and its associated aqueducts. This works is unique in Scotland in that it is the only large water works that does not have a filtration stage as part of the treatment process. Apart from disinfection and the addition of chemicals to reduce the tendency of the water to pick up contamination (such as lead) from pipes, Milngavie works remains almost exactly the same as when it was built by the Victorians. When the extreme rainfall event occurred on 31 July it was quickly noted that the water emerging from the aqueduct supplying Mugdock reservoir had a very high turbidity i.e. it was cloudy. Mugdock reservoir is one of two raw water storage reservoirs at Milngavie treatment works. Mugdock reservoir provides some 7 days storage at normal throughputs so the turbid water was not likely to reach the intake tower leading to the treatment works for some time. It was likely that the turbid water would also be much diluted by the time it reached the intake tower. Nevertheless, key staff in Scottish Water recognised that the turbid water might also pose a
Cryptosporidium threat. Accordingly, they accelerated the turn around time for
Cryptosporidium analysis from 72 hours to 24 hours as required by the Cryptosporidium Directions. They also set in train plans to limit the area supplied from Mugdock reservoir. The subsequent changes to the water distribution system in Glasgow were unprecedented. In addition, spare treatment capacity at other water works around Glasgow was utilised to reduce the demand on the Milngavie system. The work on the distribution system reduced the population potentially receiving the affected water from nearly 700,000 to around 160,000 people. The reduction in the population potentially affected also meant a huge reduction in the logistical exercise needed to manage the incident. Unfortunately despite significantly reducing the population at risk, communication problems between Scottish Water and its customers occurred which adversely affected the public's perception of Scottish Waters handling of the incident.
Following this incident, the DWQR was asked to prepare a report for the 'Ad Hoc group of Ministers on Health and Public Supply'. The initial media response to these events lead to wide ranging comment in the media covering the specific incident but also other issues of concern. In response to this the DWQR prepared an "Initial situation report on public health issues with respect to water supply across Scotland" published in August 2002. The report can be found on the Scottish Executive website at the following address:
http://www.scotland.gov.uk/library5/health/ministerdwqr.pdf
The final report on the Edinburgh and Glasgow incidents was published in January 2003 and appears on the Scottish Executive website at the following address:
http://www.scotland.gov.uk/library5/environment/dwqrr.pdf
The Ad Hoc group of Ministers also prepared a report covering wider issues which appears at the following address:
http://www.scotland.gov.uk/library5/health/watersupply.pdf
In addition to this, the Water Industry Commissioner also conducted his own investigation into how Scottish Water handled both the event and their customers with regard to supplying information and alternative water supplies. The Commissioner's report also appears on the Scottish Executive website and can be accessed at the following address:
http://www.scotland.gov.uk/library5/environment/wicfinal.pdf
Edinburgh August 2002:
An extreme rainfall event took place on 31 July, which seriously challenged the water treatment process at a number of water treatment works across Scotland. One of the works affected was Fairmilehead Water Treatment Works. This works consist of slow sand filters of Victorian vintage, which provide about half of the works output, and a more modern set of eight rapid gravity filters. The incident at Fairmilehead on 6 August was triggered by a fault that occurred while one of the rapid gravity filters was washing. A computer controlled process normally washes the rapid gravity filters every 24 hours but a fault occurred that caused one of the filters to go into a permanent wash mode. This failure caused the turbidity to rise in the water leaving the rapid gravity filters.
The rise in turbidity triggered the treatment work operators to take a water sample for
Cryptosporidium analysis. This sampling was in accordance with standard operating protocols. The sample was positive and despite correcting the fault that had occurred with the filter washing process, further positive results were recorded. However, at no time did the Health Authority conclude that the water was unfit for human consumption.
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