A diuretic is a substance that increases the rate at which water is excreted through urination. Examples of diuretics include ethanol, caffeine, water, dopamine, etc. Different classes of diuretics affect a person differently. Loop diuretics prevent the kidney from reabsorbing sodium. Thiazide diuretics increase the loss of sodium and chlorides through urination and in the process water is also lost. Diuretics are used in the treatment of conditions such as hypertension, acute renal failure, liver disease, glaucoma, etc.