Diuretic effect. Computer artwork showing the effect of diuretics (grey barriers) on a renal tubule (red) inside the kidney. These tubules regulate the levels of sodium (orange), potassium (purple) and chloride (green) ions in the filtrate before it is excreted as urine. A diuretic is any substance that encourages this excretion. Some diuretics inhibit the kidney's ability to reabsorb sodium so that the body must rid itself of the sodium and the water goes with it in the urine. Others, such as the thiazide diuretics, enhance the secretion of sodium and chloride so the body will try and rid itself of these substances in the same way. Diuretics can be used to treat heart failure, cirrhosis of the liver and hypertension (high blood pressure).