Yes, you can drink water before a glucose test. For fasting glucose tests and glucose tolerance tests, it is generally allowed and even recommended to drink water before the test to stay hydrated and make the blood draw easier. However, no other food or drink should be consumed before the test, and during the test itself you should avoid eating or drinking except for the glucose solution and water sips if allowed by your provider. Always follow specific instructions given by your healthcare provider or the testing facility. Drinking water does not affect the accuracy of the glucose test and is usually permitted up until the time of the blood draw.