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4.5 Drinking Water Quality in the Islands (Western Isles, Orkney and Shetland)

Treatment Works

Table 4.5-a Summary of Samples Taken from Water Treatment Works in the Islands

Sample compliance at water treatment works in Orkney, Shetland and Western Isles improved in 2007 (Table 4.5-a). The one E.coli detection occurred at North Ronaldsay in Orkney, and was associated with the incident of August 2007, described below. The single turbidity exceedence occurred at Cullivoe on Yell, Shetland. This treatment works is not compliant for other parameters and is due to be replaced by Scottish Water when it rationalises the three treatment works on Yell.

Table 4.5-b Summary of Disinfection Indices at Treatment Works in the Islands

The disinfection index ( DI) is used by the DWQR to track the progress being made by Scottish Water in improving control of its disinfection processes. This is to make sure that all supplies are thoroughly disinfected to keep them safe, while at the same time, limiting the extent to which chlorine concentrations fluctuate. Inconsistent chlorine residuals in water leaving treatment works are a major cause of taste and odour complaints from consumers. The higher the DI, the less consistent the chlorine level in water leaving the treatment works. Scottish Water is funded to undertake work to ensure all water treatment works have a DI of less than 100 by 2010. Although regulatory sample compliance in the islands has improved, there was a slight deterioration in performance in 2007 as far as the disinfection index was concerned (Table 4.5-b). This is in contrast to the trend seen in other regions.

Distribution System

Table 4.5-c Summary of Samples taken from Service Reservoirs in the Islands

*95% samples shall not contain coliforms; 100% shall not contain E.coli

Microbiological compliance in the Island Region improved in 2007. Coliforms were detected at nine different storage points but all storage points met the regulatory requirement that 95% of samples are free of coliforms (Table 4.5-c). The two samples containing E.coli were both from Holland reservoir on North Ronaldsay and were associated with the August contamination incident.

Table 4.5-d DMI in the Islands - Supply Zones not scoring 100%

Cullivoe supply zone on Yell, Shetland scored the lowest DMI in the Islands. This was mainly due to the poor performance of the works, mentioned earlier. Iron and manganese failures depressed the DMI score in Lerwick supply zone (Table 4.5-d).

Iron was a particular issue in Lerwick, and extensive rehabilitation work is now underway. An especially severe discoloured water issue in the Lover's Loan area of the town was resolved following the initiation of enforcement action by DWQR. Figure 4.5-a co-relates DMI and contacts to Scottish Water by consumers concerned about discoloured water.

Figure 4.5-a DMI and Consumer Discolouration Contacts in the Islands

Consumer Contacts

Figure 4.5-b Consumer Contacts about Drinking Water Quality in the Islands

The Island region recorded a higher rate of contacts about water quality in most categories (Figure 4.5-b), but especially discolouration and chlorine taste and odour. To some extent this is unsurprising as a relatively low number of contacts in this sparsely populated area will produce a high contact rate. However, there were undoubtedly a number of issues concerning the acceptability of the water to consumers during 2007.

An acute but localised issue in part of Lerwick with discoloured supplies was resolved following mains rehabilitation work by Scottish Water after DWQR had threatened enforcement action in September 2007. Also in Shetland, Cullivoe and South Yell supply zones, both on the island of Yell, experienced discolouration contact rates well in excess of 200 per 10,000 population. Due to the small populations involved this only equated to a total of 16 contacts, but is significant nonetheless because it is mainly due to the poor performance of the two water treatment works concerned. Scottish Water has committed to improving the situation by March 2009. Ness in the Western Isles also generated a significant number of discoloured water contacts during 2007 - 65 in total, giving a complaint rate of 552 per 10,000 population.

The chlorine taste and odour contact data for Scotland in 2007 is dominated by complaints from Mainland Shetland, specifically the Eela Water and Lerwick supply zones. These occurred mainly in the late Spring and Summer following a change by Scottish Water in the method it used to disinfect the water, when these supplies were switched from chlorination to chloramination. Chloramination is used to disinfect water supplies throughout the world without any problem, however the introduction of chloramination in these two Shetland supplies triggered a large number of complaints about an unpleasant taste and, in some cases, a burning sensation. Scottish Water has investigated these complaints but the solution has, to date, remained elusive. The number of customer contacts has dropped off significantly but it is evident that a number of consumers are still unhappy with their water supply. The problem is not universal and some consumers on the supplies are content with the new arrangements, nonetheless, DWQR is committed to investigating this matter until it is resolved satisfactorily. The solution however, make take time to identify.

South Uist and Benbecula in the Western Isles recorded seven and six contacts respectively about earthy or musty tastes. Although not large numbers in themselves, they do amount to significant complaint rates per head of population for this comparatively unusual contact category.

Incidents

In 2007, two events were declared incidents in the Islands. This is three less than in 2006.

Lemreway Western Isles 13 Mar 2007 - Disinfection Failure

This incident was caused by a failure of the flow meter which controls the chlorine dosing at this treatment works. A low chlorine alarm did go through to Scottish Water's Operational Management Centre and this was passed on to the standby supervisor, however, due to previous false alarms, the standby supervisor decided not to pass the alarm on to the operator until the next day. He spoke to the senior operator the next morning but neither passed the alarm on to the site operator. The low chlorine was only therefore discovered during a routine visit by the operator some 31 hours after the initial alarm. A routine sample was taken early the next morning after the alarm had been sent but the sampler appears not to have informed anyone about the low chlorine residual, so this was a further missed opportunity and Scottish Water's Public Health Team were only informed after the problem had been fixed.Scottish Water has re-trained staff, and ensured that all alarms are attended to and that samplers report any low chlorine results to its Public Health Team. Telemetry alarms at the site have also been reviewed to ensure they are appropriate.

North Ronaldsay, Orkney 08 Aug 2007 - Microbiological Failure

Following exceptionally heavy rainfall, E.coli and Cryptosporidium were detected in a number of samples taken from the supply. A boil notice was issued on 9 August and lifted on 14 September once passing samples had been obtained. Scottish Water has installed temporary filtration at the site to provide protection until a permanent solution to securing water quality is identified.

Water Quality in Local Authorities in the Islands

Comhairle Nan Eilean Siar

Water Supply Zones in Area

Quality of Public Water Supply

Summary of Private Water Supplies

Orkney Islands Council

Water Supply Zones in Area

Quality of Public Water Supply

Summary of Private Water Supplies

Shetland Islands Council

Water Supply Zones in Area

Quality of Public Water Supply

Summary of Private Water Supplies

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