Dimeric aluminum compounds and their use

A method of clarifying waters containing turbidity causing components and having an alkalinity of at least 115 ppm, calculated as CaCO.sub.3, which comprises:

• a. Adding thereto, to form a treated water, an effective amount for the purpose of clarifying said waters of a low-basicity polynuclear aluminum species with a basicity ranging between about 8.3% up to 33% and having the formula:
• Al.sub.n (OH).sub.m Z.sub.3n-m
• wherein, n is at least 1.0
• Z is a halide chosen from the group chloride, bromide, iodide, and mixtures thereof, and
• wherein the ratio of m/n ranges between about 0.25 to about 1.0 and at least 25 mole percent of the polynuclear aluminum species above has n equal to 2.0, and then,
• b. Allowing sufficient time to form and build a floc dispersed in the treated water, which floc contains turbidity causing components, and then,
• c. Phase separating the floc from the treated waters to obtain clarified water.