Water is one of the most important natural resources found in the world. Therefore, population growth and higher living standards will cause ever increasing demands for good water quality in the future, exerting an extreme pressure in water resources. Water is essential for supplying domestic, municipal, industrial, and agriculture needs. Furthermore, while growing populations and increasing water requirements are a certainty, it is not known how climates will change and at what extent they will be affected by man's activities. This volume contains the scientific papers presented at the 4th International Conference on Water Resources Management, held in Kos, Greece. The scientific topics presented at the Water Resources Management 2007 conference include: water management and planning, hydrological modelling, water quality, groundwater flow problems and remediation, waste water management, waste water treatment and management, water markets and policies, pollution control, irrigation problems, urban water management, decision support systems and coastal and estuarial problems.