A water-cooled ESC is going to set you back about 10-50% more then a regular ESC depending on the make. Here now, you can make something similar for almost nothing.
Step 1: Materials
Stuff you'll need--
2) Aluminium sheet metal
3) brass tube
4) Heat sink paste
The ESC, you'll obviously need one.
The aluminium sheet metal, I used a small 2mm thick piece cut down to fit the dimensions of my ESC. 1 or 1.5mm will work too.
The brass tube, it's 4mm wide, salvaged from an old telescopic antenna. (That's why they look shiny chromed in my pics)
The hear sink paste, Its a heat conducting compound, something you might have to buy. Should be easily available in electronics stores.
Step 2: Building the Radiator
Then, cut down the brass tubes making sure 10-20mm of it protrudes out of the aluminium plate and superglue them to plate leaving some space in between.
Now, add a generous amount of heat sink compound between the tubes and make sure you get the paste into every nook and cranny for maximum heat conduction and better cool.
You'll need to cut another piece of aluminium, drill a central hole and run an appropriate screw through it down to the base plate and secure the tubes.
Your water-cooling radiator is done!
Step 3: Mounting the Radiator on an ESC
Then, on the flat surface of your ESC, you need to strip off the heat shrink sheath to expose the metal heat sink plate inside.
Apply a not-too-thick layer of heat sink compound to the exposed surface of the ESC and the base of the radiator, affix both the surfaces and run a very thin bead of superglue along the perimeter of the mating seem to secure the radiator to the the ESC.
And that's it! Your ESC water-cooling radiator is done and ready to run!
Step 4: Aesthetics!
I masked off the ESC part and sprayed a coat of matt black aerosol paint. Neat, ain't it?
And then, down to business! Installed the water-cooled ESC in my scratch built RC air boat "Satanic" and gave it a run in the pond, worked like a charm.
Good luck, DIYers!