How much heavy water do you want?
First you need to have a very long electical spark in the range of several million volts.
http://home.earthlink.net/~gary350/tc10-4.jpg
Next you have to direct the high voltage spark along a straight line with magnets along the path of the spark. Line up several magnets in opposite order along the path, N, S, N, S, N, S, N, S, N, S, etc. this removes all the electrons and protons from the spark leaving only the neutrons.
The neutrons are shot into water now you have to slow them down other wise they travel all the way through the water and out the other side. I have forgotton how to slow down neutrons but if I remember correctly I beleive you use a block or grafite or lead I can not remember.
After you saturate the water with neutrons you have heavy water.
NOW......what are you going to do with heavy water? You could build an atomic hand grenade and throw it across the back yard.