8.7.1 Forms and records
An individual record must be produced for each site inspection or sample and should include the location and reference of the sampling site (that should ideally be equal to the code number of the sample), the date, the time, weather conditions, tide, water temperature, results of visual inspection for abnormal conditions, sources of contamination and the name of the inspector or sampler. Sampling records should also list the laboratory procedures and results (method of analysis, dilutions or volumes analysed, time of analysis, results for each step, any anomalies in the analysis of results and the name of the analyst). Ideally, record forms should occupy a single page. Forms should be conveniently archived, because they will be used later by the data handlers for transcription to the database and they will be analysed for the purposes of preparing the report of the monitoring or survey programme. Great care should be taken in preparing the report and its contents and format should be agreed by those responsible for analysis, data handling and for reporting results and, if necessary, by those responsible for co-ordinating results of regional, national and international programmes. For quality assurance, it should be possible to conduct an “audit trail” through the whole process of visiting the site, analysing the sample and filing the results on the database (see Chapter
. An example of a record form for site inspections is given in Box 8.1.
Recording results of microbiological analyses
The results of microbiological analyses of water quality must always be regarded as an estimate of the water quality at the time and site of sampling, rather than as an absolute determination (PHLS 1994, APHA/AWWA/WPCF, 1995). All enumeration methods depend on the assumption that bacteria and other micro-organisms are randomly distributed in water samples and that the samples conform to the Poisson distribution (see Chapter 3). In reality, the clumping of bacteria and their aggregation on particles cause samples to depart from the Poisson distribution, thereby introducing additional error. There is little that can be done to reduce this error, apart from taking representative samples (free of sediment and other solid matter) and mixing the contents of the sampling bottles vigorously before taking sub-samples for analysis. It has been shown that two halves of the same sample can vary widely in the counts observed (PHLS, 1994).
A historical record of water quality in a bathing area, in normal and extreme situations, enables the selection of the most appropriate dilutions and facilitates the correct enumeration of the final density of indicator organisms that has to be reported as the total number of cfu per 100 ml.
Great care should go into the counting and recording of analytical results in order to avoid recording results wrongly, leading to errors that can result in statistical misinterpretations of water quality at the recreational area. Typical sources of error in the laboratory are caused by operator fatigue and mistakes, such as mislabelling of bottles, Petri dishes and tubes, and errors in preparing and transferring volumes and dilutions of samples. Because labels attached to the lids of Petri dishes, tubes and bottles can be transposed, the labels should be placed on the dish, tube or bottle itself, because these contain the culture medium. Although it may not be obvious, operators vary in the accuracy with which they count colonies and, in addition, unsuspected partial colour blindness can interfere with the interpretation of biochemical reactions of target colonies