Yes, you can usually drink plain water while fasting for most blood tests. Always follow any specific instructions your own doctor or lab gave you, because there are occasional exceptions.
What you can drink
For standard fasting blood work (like glucose, cholesterol, basic metabolic panel), guidelines typically allow and even encourage: plain, unflavored still water only. Water does not contain calories or nutrients, so it does not affect common fasting labs.
What to avoid
You should not have:
- Juice, soda, milk, coffee, or tea (even black), because ingredients like sugar, caffeine, and proteins can change test results.
- Flavored or carbonated waters, or water with lemon or sweeteners, as additives can also mildly affect digestion or lab values.
Extra tips
Staying well hydrated with water can make your veins easier to find and may make the blood draw more comfortable. Most fasting windows are 8–12 hours, so if unsure, confirm the exact fasting instructions with your clinic.
