Solar thermal distillation of saline water is an effective way to meet the clean water demands of remote and rural population. Multi-effect solar stills have been widely acknowledged for their high distillate productivity. Most of the multi-effect solar stills studied are of horizontal type which has reduced distillate yield compared to vertical multi-effect diffusion solar stills. In this work, a new configuration of vertical diffusion multi-effect solar still has been proposed and it has been optimized using transient mathematical modelling. The feed water separately heated in solar collector is distributed equally in all effects such that glass reflectors, heat pipes which were used for heating the first effect of previous configurations have been avoided which increases the safety and handling flexibility of the present unit. The optimum number of effects and diffusion gap was found to be 5 and 10 mm, respectively. The distillate yield from the unit was highly dependent on the diffusion gap, mass flow rate of feed water circulated through the solar collector and feed water salinity. Distillate yield was found to decrease with the increase in salinity of feed water and maximum distillate yield was recorded as 8.25 kg/m²-d and 6.07 kg/m²-d during summer for feed water with 0 and 10 wt% salinity, respectively. The yield from the unit supplied with hot feed water from evacuated heat pipe solar collector is higher than the yield from the unit supplied with hot feed water from solar flat plate collector.