Diuretics increase the amount of urine passed, which causes the body to lose water and salt.
Water pills cause you to urinate more often. This increases the rate at which urine and salt leave the body, thereby reducing blood pressure. It is not a cure. Side effects that usually do not require medical attention include constipation, dizziness or lightheadedness, headache, increased sensitivity to the sun, loss of appetite, stomach upset, pain, or cramps. If any of these effects become bothersome, they should be reported to your doctor.