The first step in the treatment of surface waters to drinking water is the removal of suspended solids and colloids (particles <1 μm in diameter) from the water. For this purpose, the surface water is subjected to so-called coagulation and flocculation with the aid of chemicals. The optimum pH for this treatment is often below pH 7.4. Raw waters of medium to high alkalinity therefore benefit from a pH adjustment with acids in order to reduce the consumption of expensive chemicals and the associated production of waste sludge. In addition, when coagulating with aluminum salts, a well-adjusted pH value helps to keep the residual aluminum content low. This also reduces the aluminum load of any downstream activated carbon filter.