Aluminum is found in a variety of minerals in the earth's crust.  The metal and its alloys have many uses, including heat exchangers, construction materials, and aircraft parts.  Alum (aluminum potassium sulfate) is used in water treatment to flocculate suspended particles, but may raise the level of aluminum in the finished drinking water.  The maximum secondary contaminant limit for drinking water is 0.05-0.2 mg/L.

The Colorimetric Method
The Aluminum Vacu-vials^® test method is based on the reaction between aluminum and Eriochrome Cyanine R (ECR), which forms a red dye-lake at approximately pH 6.0 in proportion to the amount of aluminum present in the sample.  Results are expressed as ppm (mg/L) aluminum.