Can I drink plain water before measuring my blood sugar?

Before measuring blood glucose, it is generally acceptable to drink a small amount of plain boiled water; however, excessive water intake should be avoided. For fasting blood glucose measurement, water intake should ideally be minimized.

Fasting blood glucose testing typically requires abstaining from calorie-containing foods—including staple foods, dairy products, meat, and eggs—but usually does not restrict water consumption. Nevertheless, beverages with high sugar content—including sweetened drinks or water with added sugar—must be avoided, as they may interfere with test accuracy. If thirst is severe, a small amount of plain boiled water may be consumed; since it contains virtually no calories, it generally does not affect blood glucose results. However, excessive water intake can dilute the blood and lower blood glucose concentration, potentially leading to inaccurate test results. Therefore, water intake should be minimized when measuring fasting blood glucose.

In addition to avoiding sugary beverages, water with added sugar, and excessive water intake before blood glucose testing, patients should also avoid consuming overly sweet, spicy, greasy, or otherwise irritating foods. They should maintain a calm and stable emotional state and avoid emotional excitement, which may elevate blood glucose levels. If diabetes is suspected, in addition to fasting blood glucose testing, patients are typically advised to undergo an oral glucose tolerance test (OGTT) or a 2-hour postprandial blood glucose test.