Patients can drink small amounts of water while fasting for blood work, according to St. Michael's Hospital. Fasting prior to blood work is necessary when a patient has fasting glucose, fasting triglycerides, fasting lipids and glucose tolerance tests.
Patients fasting prior to blood work should not eat or drink anything for 12 hours before the test, notes St. Michael's Hospital. Small amounts of water are permissible, and patients can take their regular medications unless their doctor tells them not to do so. Patients must refrain from smoking, chewing gum, drinking coffee or tea, and exercising, as these activities can affect blood test results.