title: [Monitoring microbiological safety of small systems of water distribution. Comparison of two sampling programs in a town in central Italy].
abstract: OBJECTIVE
  To determine the frequency of sampling in small water distribution systems (<5,000 inhabitants) and compare the results according to different hypotheses in bacteria distribution.
  
  
  METHODS
  We carried out two sampling programs to monitor the water distribution system in a town in Central Italy between July and September 1992; the Poisson distribution assumption implied 4 water samples, the assumption of negative binomial distribution implied 21 samples. Coliform organisms were used as indicators of water safety. The network consisted of two pipe rings and two wells fed by the same water source. The number of summer customers varied considerably from 3,000 to 20,000.
  
  
  RESULTS
  The mean density was 2.33 coliforms/100 ml (sd= 5.29) for 21 samples and 3 coliforms/100 ml (sd= 6) for four samples. However the hypothesis of homogeneity was rejected (p-value <0.001) and the probability of II type error with the assumption of heterogeneity was higher with 4 samples (beta= 0.24) than with 21 (beta= 0.05).
  
  
  CONCLUSIONS
  For this small network, determining the samples' size according to heterogeneity hypothesis strengthens the statement that water is drinkable compared with homogeneity assumption.
authors: Agenzia di sanità pubblica della Regione Lazio, Roma.
authors: Paolo
authors: P
authors: Papini
authors: Annunziata
authors: A
authors: Faustini
authors: Rosa
authors: R
authors: Manganello
authors: Giancarlo
authors: G
authors: Borzacchi
authors: Domenico
authors: D
authors: Spera
authors: Carlo A
authors: CA
authors: Perucci