Water samples can be taken in a variety of ways:
Water-sampler: Water samplers are used to collect seawater samples in situations where direct contact with the water body cannot be made e.g. from the deck of a large vessel. The sampler is mounted to a weighted hydrowire and closed at the desired depth by a dropping weight. The sampler collects a vertical segment of water. Following recovery of the sampler, the water sampler is discharged into an appropriate laboratory sample container.
Sample bottle: Water samples can be collected directly into a sample bottle where contact with the waterbody can be made e.g. streams, accessible rivers and lakes and from a RIB or inflatable. The sample bottle is simply lowered by hand into the water and left to fill.
Bailers: Bailers are used to sample ground water monitoring wells to retrieve water samples from below the ground surface. They consist of a high density polyethylene hollow tube with a handle at the top and a check valve at the bottom. A tether cord is attached to the handle of the bailer and the bailer is lowered into the well where it comes into contact with the groundwater.
The weight of the bailers cause them to sink into the water. The hydrostatic pressure of the water pushes up on the check valve (usually a ball check) causing the valve to open and water to flow into the tube. When the bailer has filled to its submerged level the valve closes, preventing water from escaping. The bailer is retrieved using the tether and the sample discharged to an appropriate laboratory sample container.