water samplers can be either automatic out or manually operated. Automatic samplers are used to collect samples at either fixed time-intervals or in proportion to the flow and then to retain the eater sample in a separate container. These are commonly used, for example, in rivers or from a point source (effluent outfall). These are commonly used, for example, in rivers or from a point source (effluent outfall). In addition,automatic samplers can be used to allow the collection of time-averaged samples or precipitation. In the case of the latter, the onset of rainfall triggers the collection mechanism.Manually operated samplers are essentially open tubes of known volume (typically l to 30 l) fitted with a closure mechanism at each end. They are constructed of stainless-steel or PVC. Manually operated samplers are particularly useful when sampling form open waters (e.g. oceans, seas, lakes, etc.) at specific depths. The sampling device is lowered on a calibrated line to the specific sampling depth, the sample is taken and then top and bottom lids are closed and sealed.