Dear Khaleel

I agree with Dr Maine totally. The problem is not in increasing the still basin area. Of course, increasing the basin area will increase evaporation. However, the problem in reducing the condenser (here I mean the glass cover) temperature to increase the condensation. Reducing the glass cover temperature can be achieved by spraying spray water from period to period or by putting a fan to move the air and increase the forced convection above the glass cover. In the first option you will use brackish water which will reduce the sun's rays due to the dirt accompanying to it, resulting in still productivity reduction sometimes. The second option needs electrical energy to run the fan and can be obtained from  a solar cell source, thereby reducing the need for regular energy

In my view it's more a problem of getting the heat away from the steam rather than just increasing the surface area. What sort of end use heat sink are you using? The incoming water? Air? Ground?

Dear Khaleel

I agree with Dr Maine totally. The problem is not in increasing the still basin area. Of course, increasing the basin area will increase evaporation. However, the problem in reducing the condenser (here I mean the glass cover) temperature to increase the condensation. Reducing the glass cover temperature can be achieved by spraying spray water from period to period or by putting a fan to move the air and increase the forced convection above the glass cover. In the first option you will use brackish water which will reduce the sun's rays due to the dirt accompanying to it, resulting in still productivity reduction sometimes. The second option needs electrical energy to run the fan and can be obtained from  a solar cell source, thereby reducing the need for regular energy

Dear sir Maine and sir Miqdam   i thank you for your answers and i agree your answers  

is vacuum still is good