Another aspect that ecosan systems are trying to address is the possible upcoming shortage of phosphorus. Phosphorus has an important role for plant growth, and therefore in fertilizer production, but is a limited mineral resource. The situation is similar for potassium. Known mineral phosphate rock reserves are becoming scarce and increasingly costly to extract – this is also called the "peak phosphorus" crisis. One review of global phosphate supply suggested that if collected, phosphate in urine could supply 22% of the total demand.