The effect of drinking water on blood tests depends on how much water you drink, a small amount has little effect, but it is recommended that you try not to drink water. Blood test is the main clinical examination, can provide more accurate data basis for the diagnosis of a variety of diseases. Drinking a small amount of normal water will not have a special effect on blood tests. If a large amount of water is drunk, causing blood dilution, it will affect the test results. For example, in the case of common anemia diagnosis, if a large amount of water is consumed before the blood test, the water can be rapidly absorbed into the bloodstream and the blood is diluted, resulting in the concentration of the tested blood substances being affected, and the test will show a decrease in the count of red blood cells and a decrease in the content of hemoglobin, which will have a certain impact on the diagnosis. Communicate with your doctor in a timely manner before the blood test, and eat, drink and exercise according to the regulations, so as not to affect the accuracy of the test results, and to reduce the adverse effects on the diagnosis of the disease.