Tannin-based coagulant agent called Silvafloc was tested on surface river water clarification. This novel coagulant can be used in drinking water treatment, and consist of a chemically modified tannin extract from Schinopsis balansae, commonly known as Quebracho colorado. Low coagulant doses reached high turbidity removal percentage and operational conditions of neutral pH and room temperature allow up to 90% turbidity removal with 20 mg L-1 of coagulant. Rapid and slow mixing periods in Jar test as well as stirring intensity were evaluated and they were found to be less influent than coagulant dosage. Silvafloc drives to a significative disinfection (around 99.9% for fecal streptococcus and fecal conforms and up to 70% for total coliforms). Treated water also presented very low content in polyphenols (about 0.4 mg L-1) and organic matter content was not increased, but removed about 30%. If compared with other natural or inorganic coagulants, Silvafloc is more efficient than aluminium sulphate, a classical metal salt for water clarification. (C) 2010 Elsevier B.V. All rights reserved.