Most diseases require blood tests when you go to the hospital. If you are doing a routine blood test or want to check your blood type, drinking water before the test will have no effect. However, if you need to do blood lipid, blood sugar, liver and kidney function tests, you should fast for at least 8 hours before the test to ensure the accuracy of the test results. It is also important to note that the day before the test, you should not eat too greasy food, and you should not drink alcohol, and it is also best not to smoke. There are also some special requirements that the doctor will give special instructions during the appointment.