You can drink small amounts of water during a blood glucose measurement, but not large amounts. Blood glucose is usually measured by taking blood from a vein or peripheral blood, so if you drink a lot of water during or before the measurement, it may affect the accuracy of the results. However, drinking only a small amount of plain water does not usually have a significant effect on blood glucose, so it is okay to drink a small amount of water during a blood glucose measurement, but it is not recommended to drink a large amount. It should also be noted that fasting blood glucose needs to be measured after an overnight fast of 8 to 10 hours, and two-hour postprandial blood glucose needs to be calculated two hours after the first bite of food. If abnormal blood glucose values occur, it is recommended to go to the hospital and ask the doctor to make a judgment.