Glucose tolerance generally refers to the oral glucose tolerance test. If the amount of water consumed during the oral glucose tolerance test is low, the test can be continued, but if the amount of water consumed is too high, the test may need to be repeated. Fasting is required for 8 to 10 hours before the oral glucose tolerance test. If you drink water during the oral glucose tolerance test, it is usually not a big deal if you just have one or two sips of water, and you can continue with the test. However, if a large amount of water is consumed, the test may need to be repeated because large amounts of water will dilute the blood and affect the accuracy of the results. It is advisable to inform your doctor after drinking water during an oral glucose tolerance test so that he or she can determine whether a retest is necessary.