The document discusses three types of water samples: grab samples, composite samples, and integrated samples. A grab sample is a discrete sample collected at a specific time and location from a source that must be constant. A composite sample is a mixture of grab samples that may be measured or random samples collected at different times, and is useful for temporal variations in water quality. An integrated sample is a discharge-weighted sample collected from different points or depths due to horizontal or vertical variations in a river, which requires special equipment.