Microbiological water quality requirements for salad irrigation in the United Kingdom

The growth in United Kingdom salad production is dependent on irrigation to maintain product quality. There are concerns that irrigation with poor-quality water could pose a disease risk. This article examines the key issues in the emerging debate on the microbiological quality of water used for salad irrigation in the United Kingdom. The links between irrigation water quality and foodborne disease, and the current international guidance on irrigation water quality, are firstly reviewed. The findings indicate that a number of recent food-poisoning outbreaks have been linked to the consumption of fresh fruits and vegetables and that unhygienic product handling is implicated as the principal source of contamination. There is also credible evidence that salads contaminated in the field, including by irrigation water, can pose a small disease risk at the point of sale. Although irrigation water-quality standards exist in various forms internationally, there is no nationally agreed on standard used in the United Kingdom. This paper then describes the results of a survey conducted in 2003 of United Kingdom irrigation practices that might influence the microbiological quality of salads. The survey showed that surface water is the principal irrigation water source, that overhead irrigation predominates, that the gap between the last irrigation and harvest may be < 24 h in many cases, and that current water-quality monitoring practices are generally very limited in scope. This paper concludes with a discussion of the issues emerging from the review and survey, including the need for improved water-quality monitoring, and the problems associated with establishing water-quality standards that could be either too strict or too lax.