This paper presents an original method for finding the most economically advantageous choice for the installation of micro hydroelectric plants. More precisely, the paper that follows is to be considered in a context defined as "problematic" by those who have the job of constructing water-flow plants with only small head and modest flow rates. With these initial data one can see immediately that the specific energy of the fluid is low and it is therefore necessary to elaborate large masses of water in order to obtain work, and therefore a return, to render such an investment profitable. Traditional plant solutions using Kaplan or Francis type turbines must be rejected because of the high levels of initial investments. Much more simple configurations must be analysed, such as plants with propeller turbines or Michell-Banki turbines, in order to reduce the investment costs. The general methodology applied provides a powerful decision-making instrument which is able to define the best plant configuration. The method is based on the use of economic profitability indicators, such as the Net Present Value (NPV), calculated using the plant project parameters, the nominal flow rate and head, and the particular hydrologic characteristics of the site, such as the type of distribution, the average value and the standard deviation of the flow rates in the course of water supplying the plant. A numerical example for a plant situated in the Emilian Appennine Range then makes it possible to demonstrate the simplicity and applicability of the proposed method. (C) 2003 Elsevier Science Ltd. All rights reserved.