It is best not to drink water before the blood test. Drinking small amounts of water generally does not affect the results of blood tests, but if a large amount of water is consumed it may cause dilution of the test indicators and affect the test results. The reference values of many items are set in the fasting state, if you drink a lot of water before the blood draw, it will lead to the test results are lower than the actual. Moreover, many times in addition to blood tests doctors will also prescribe imaging tests, such as ultrasound, etc., if you drink more water may lead to gallbladder contraction, intestinal peristalsis gas interference, and make ultrasound can not be carried out.