Guidelines for safe recreational water environments
Volume 1 : Coastal and fresh waters
Faecal pollution and water quality
The most frequent adverse health outcome associated with exposure to faecally contaminated recreational water is enteric illness. A cause–effect relationship between faecal or bather-derived pollution and acute febrile respiratory illness (AFRI), which is a more severe health outcome than gastroenteritis, has also been shown.
There is consistency in the overall body of evidence concerning health effects from faecally polluted recreational waters, and a series of randomized controlled trials performed in the United Kingdom form the key studies for derivation of guideline values for the microbiological quality of recreational waters. For marine waters, only intestinal enterococci (faecal streptococci) showed a dose–response relationship for both gastrointestinal illness and AFRI. The guideline values are expressed in terms of the 95th percentile of numbers of intestinal enterococci per 100 ml and represent readily understood levels of risk based on the exposure conditions of the key studies.
There is inadequate evidence with which to directly derive a water quality guideline value for fresh water. Application of the guideline values derived for seawaters to fresh waters would be likely to result in a lower illness rate in freshwater swimmers, providing a conservative guideline in the absence of suitable epidemiological data for fresh waters. Studies under way may provide a more adequate basis on which to develop freshwater guideline values.
The guideline values should be interpreted or modified in light of regional and/or local factors. Such factors include the nature and seriousness of local endemic illness, population behaviour, exposure patterns, and sociocultural, economic, environmental and technical aspects, as well as competing health risk from other diseases that are not associated with recreational water.
The initial classification of a recreational water environment is based upon the combination of evidence for the degree of influence of (human) faecal material (by sanitary inspection of beach and water catchment) alongside counts of suitable faecal index bacteria (a microbial quality assessment). Information to be collected during sanitary inspections should cover at least the three most important sources of human faecal contamination of recreational water environments for public health purposes: sewage; riverine discharges (where the river is a receiving water for sewage discharges and either is used directly for recreation or discharges near a coastal or lake area used for recreation); and bather contamination, including excreta. Where human inputs are minimal, investigation of animal faecal inputs should be explored.
In the microbial water quality assessment, the sampling programme should be representative of the range of conditions in the recreational water environment while it is being used. An important issue is that of collecting sufficient numbers of samples so as to make an appropriate estimation of the likely densities to which recreational water users are exposed. The precision of the estimate of the 95th percentile is higher when sample numbers are increased. The number of results available can be increased significantly by pooling data from multiple years, unless there is reason to believe that local (pollution) conditions have changed. For practical purposes, data on at least 100 samples from a 5-year period and a rolling 5-year data set can be used for microbial water quality assessment purposes.
The outputs from the sanitary inspection and the microbial water quality assessment can be combined to give a five-level classification for recreational water environments — very good, good, fair, poor and very poor. Following initial classification, it is proposed that all categories of recreational water environment would be subject to an annual sanitary inspection (to determine whether pollution sources have changed) and continued water quality monitoring.
Another component of the assessment of a recreational water environment is the possible “upgrading” of a recreational water environment if a significant change in management reduces human exposure to microbial risk.
Follow-up analyses are recommended when the intestinal enterococci counts are high but the sanitary inspection suggests low sanitary impact, or vice versa. A primary role of the follow-up is to help identify the source of the faecal pollution, thereby assisting in the assessment and management of faecal contamination in recreational water environments.
In certain circumstances, there may be a risk of transmission of pathogens associated with more severe health effects (such as infectious hepatitis or typhoid fever) through recreational water use. Public health authorities should be alert to such hazards where exposure may occur and should take appropriate action to protect public health.
Population groups that may be at higher risk of disease include the young, the elderly and the immunocompromised, as well as visiting populations susceptible to locally endemic disease. If such groups are significant water users, then this should be taken into account in risk assessment and management.
Management action in response to a recreational water environment classification indicating unacceptable faecal contamination can be both immediate, such as public health advisories, and long term, such as pollution abatement.