The existing water treatment process often uses chemicals, which is of high health and environmental concern. The present study focused on the efficiency of microemulsion prepared magnetic iron oxide nanoparticles (ME-MIONs) and protein-functionalized nanoparticles (MOCP + ME-MIONs) in water treatment. Their influence on mineral ions and microorganisms present in the surface water from lake Brunnsviken and Orlangen, Sweden were investigated. Ion analysis of water samples before and after treatment with nanoparticles was performed. Microbial content was analyzed by colony forming units (CFU/ml). The results impart that ME-MIONs could reduce the water turbidity even in low turbid water samples. Reduction of microbial content (98%) was observed at 37 degrees C and more than 90% reduction was seen at RT and 30 degrees C when compared to untreated samples from lake Orlangen. The investigated surface water treatment method with ME-MIONs was not significantly affecting the mineral ion composition, which implies their potential complement in the existing treatment process. (C) 2013 Elsevier Ltd. All rights reserved.