The fourth most common element in the earth's crust, aluminum is naturally present in drinking water and is added as a chlorination preparation at water utilities. Most of what is added is usually removed, but a residue may sometimes be passed into treated water. Aluminum may cause discoloration of water. Currently there is ongoing research and various studies on the link between aluminum in drinking water and Alzheimers Disease. The recommended treatment methods for aluminum are Distillation or Reverse Osmosis.