The production of polyaluminum hydroxychlorosulfates (PACS) suitable for effective use as flocculants and coagulants in water treatment is described. The product is a fluid, clear solution that is stable with respect to precipitation and gelling for extended periods of time. Key features of the process include: i) the production of a PACS solution of about 12-16% Al.sub.2O.sub.3 and about 40-60% basicity at moderate temperatures (50-60.degree. C.) using a zerovalent aluminum source, such as aluminum powder, ii) the addition of an alkali metal or alkali earth metal base at low temperatures (20-30.degree. C.) to produce PACS products ranging from 9-12% Al.sub.2O.sub.3 with basicities ranging from 70-80%, iii) the addition of an alkali metal base at low temperatures without the use of high shear mixing, iv) a PACS product that does not contain significant amounts of the Al.sub.13-mer Keggin complex , v) a product with greater than 80-95% of the aluminum polymers bimodally distributed in the range of 20,000-40,000 Daltons and 135-750 Daltons, and vi) the formation a PACS whereby greater than 95% of the sulfate is bound to aluminum and is contained in the aluminum polymers distributed in the range of 20,000-40,000 Daltons.