Turbidity tubes for drinking water quality assessments

Turbidity tubes have been considered to be the field method of choice for drinking water quality monitoring in resource-limited contexts because of their relative simplicity and low cost in comparison with conventional (nephelometric) turbidimeters. These tubes utilise the principle of visual extinction of a submerged target for turbidity determination and were therefore thought to be subject to user subjectivity, possibly affecting results. This study evaluated their performance under both field and controlled-laboratory conditions. Results from turbidity tubes can differ substantially from those obtained with conventional turbidimeters; this is of particular importance in the reporting of low turbidity (<10 NTU) measurements. These differences could be due to a combination of factors, such as: user variability, differences in calibration scales, and turbidity tube target shape and background colour. In view of their limitations, the usefulness of turbidity tubes for drinking water quality assessments and recommendations on the reporting of their results are also discussed.