The Basic Sediment and Water (BS&W) is a term originally used to refer to the measurement of water and sediment (suspended solids) in crude oil production. Measurement can take place at the wellhead, tank or at custody transfer. Today, the term is also used interchangeably with "water cut" - or the percentage of water in crude oil.

Usually, the BSW and Gas Sampling Kit is run parallel to a well test or production test. The origin of the design of this tool came from the way BS&W sampling was done. The measurement of gas volume has been incorporated as knowing the gas/oil ratios (GOR) of a well test or production test is a control of the efficiency of the flow process or the character of a well. Many times critical information, like the GOR, gets lost due to the well not producing according the design of the well test or production set up.