Watermelon is a natural diuretic which helps increase the flow of urine, but does not strain the kidneys (unlike alcohol and caffeine). Watermelon helps the liver process ammonia (waste from protein digestion) which eases strain on the kidneys while getting rid of excess fluids.Watermelons have an alkaline-forming effect in the body when fully ripe. Eating lots of alkaline-forming foods (fresh, ripe, fruit and vegetables) can help reduce the risk of developing disease and illness caused by a high-acid diet (namely, meat, eggs and dairy).