The software is a calculation program, according to known and tested method in water treatment speciality : HALLOPEAU & DUBIN method, to modify and supplement by the author (Pierre Ravarini). EQUILWIN software can calculate calcocarbonic equilibrium in water. It allows to characterize a water or a mixture of many waters, to establish whether a scaling water, aggressive or balance and determine appropriate treatment to reduce this water balance, or to test various treatments. The proposed treatments are those that are usually found on plants for drinking water production. This software was developed by Pierre RAVARINI, engineer / hydrologist specialist water treatment and in particular carbonic equilibrium, according to the principles of the Hallopeau-Dubin method, supplemented by the author. Development principles and general ergonomics have been largely inspired by Equil program (implemented in QBasic).