Dams increase water supply by storing and saving the surplus floodwaters. It is the barrages whose canals take water directly from the rivers, there being no storage, which drain rivers. The 13 canals drawn from the Guddu, Sukkur and Kotri barrages are the ones that are causing shortage of water at the tail ends. Unless more dams are built, our existing river flows and two dams cannot cope with the ever-increasing demands of our population. Conservation methods like lining of canals etc, will save water only during the three wet months but we cannot store water through these methods in the nine dry months. The only remedy is building more storage while the glaciers last. -KHURSHID ANWER, Lahore, via e-mail, August 31.