We intend to observe the signature of water ice in the mid- and far-infrared towards high mass and low mass embedded sources in protostar regions with ISO SWS/LWS and PHOT P. Laboratory studies show that the solid water infrared features at 3.1 and 45 mu exhibit reversible and irreversible temperature effects in band shape and position. Observations of these bands towards sources embedded in dense clouds can provide constraints on the composition and thermal evolution of the ices throughout the dust shell surrounding the sources. The 3.1 mu feature will probe the environment relatively close to the star, whereas the 45 mu band monitors the very cold dust regions far from the radiating source. The 3.1 mu band has been already extensively studied by ground-based observations. Observations of the 45 mu water ice band will provide the unique opportunity to study the chemistry in environments that cannot be probed from the ground. ISO is uniquely capable of providing a complete spectrum of water ice, including bands obscured by the Earth's atmosphere, in particular the 45 mu water ice band. Laboratory simulations on water ice will be performed during ISO operations to ensure that the full diagnostic value of these observations will be achieved.