Process for making water drinkable

A process for making drinkable an aqueous solution having solids in suspension, containing a coagulation-flocculation step, characterized in that said step comprises:

• a) a step of adding coagulants to the aqueous solution to be treated;
• b) a step of stirring the aqueous solution thus supplemented;
• c) a step of separating out the coagulated solids by decantation or flotation;
• d) a step of recovering a purified water;
• and in which the coagulants added in step a) comprise metal salts chosen from ferric salts and aluminum salts and also a liquid starchy composition comprising a cationic waxy starch, said cationic waxy starch having, when it is in the form of an aqueous composition, a viscosity, measured according to a test A, of greater than 100 mPa·s and less than 1000 mPa·s, this test A consisting in adjusting the solids content of cationic waxy starch dry mass the aqueous composition to 10% and then in measuring the Brookfield viscosity at 25° C. of the resulting composition.