A Desalination Experimental Facility (DEF) comprising multistage flash (MSF) unit of capacity 15 cubic meter/day with three stages had earlier been commissioned and operated for about two years to study the basic parameters of the MSF process. On the basis of operational experience and the data collected from experiments and the information available in literature a 33 stage 425 cubic meter/day MSF plant was designed, fabricated, installed and the same is under commissioning. This prototype plant was first such unit in India. This paper gives the considerations for the design of 425 cubic meter/day prototype MSF plant and the factors to be considered for scale-up to commercial size plants. The problems experienced during the module fabrication, erection and initial startup of the plant are highlighted. © 1989.