You can drink plain water while fasting for most blood work, and it’s actually encouraged rather than forbidden.

Quick Scoop

  • Yes: Plain, still water is allowed during fasting for blood tests unless your own doctor or lab has given different instructions.
  • No: Coffee (even black), tea, juice, soda, milk, alcohol, flavored or sparkling water, chewing gum, mints, and supplements can all affect results and are usually not allowed.
  • Why water helps: Staying hydrated makes veins easier to find, can reduce dizziness, and does not change common fasting labs like glucose, lipids, A1c, basic metabolic panel, or thyroid tests.
  • Typical rule: “Nothing to eat or drink except water for 8–12 hours before the test” is the standard advice for many fasting labs.

What You Can Usually Do

Most standard fasting instructions say:

  1. You may (and should) drink plain water.
  2. Stop all calories for 8–12 hours before the test, depending on what’s ordered.
  3. Take only medications your provider said are okay with a sip of water.

Many clinics even recommend 1–2 glasses of water in the hour or two before the draw so your veins are easier to access and you’re less likely to feel faint.

What To Avoid While Fasting

Even small amounts of other drinks can stimulate digestion or change lab values:

  • Coffee (black or with cream/sugar): Caffeine and other compounds can affect glucose and other markers.
  • Tea or energy drinks: Often contain caffeine and sometimes sugar/artificial sweeteners.
  • Flavored or sparkling water: Flavors, sweeteners, and carbonation can slightly stimulate digestion and may skew sensitive tests.
  • Juice, soda, milk, sports drinks: Clearly contain sugars or calories that will affect fasting results.
  • Gum and mints: Sweeteners and chewing can trigger digestion, which some labs want you to avoid.

If you accidentally had any of these, tell the person drawing your blood; they can note it or decide if the test should be rescheduled.

Small “What If” Scenarios

  • If your doctor said “no fluids at all”: Follow their specific instructions, especially if you have heart failure, kidney disease, or fluid restrictions, because extra water can be risky in those conditions.
  • If you feel dizzy or very weak from fasting: It’s still okay (and safer) to sip water; mention how you feel when you arrive.
  • If you’re unsure about black coffee or flavored water: Treat it as “not allowed” until you confirm with your lab or doctor.

Mini FAQ (Fasting + Water)

  • “Will water break my fasting blood test?”
    No, plain water does not break a medical fasting blood test and does not alter the main fasting labs for most people.
  • “How much water is too much?”
    Normal amounts (a few glasses, e.g., 8–16 oz before the test) are fine; just don’t force very large volumes unless your doctor says so, especially if you have heart or kidney issues.
  • “Do all blood tests require fasting?”
    No. Many tests don’t require fasting at all, and some lipid panels are now done non‑fasting; your lab order or clinic should say if fasting is needed.

Information gathered from public forums or data available on the internet and portrayed here.