The guys at Mighty Car Mods have put together this awesome guide on how to build your own intercooler water spray with a variety of simple and inexpensive parts:
Better DIY Intercooler Water Spray
This solution is better, The guys at PMM show you how to make your own intercooler sprayer, decreasing intake temps and increasing horse power:
In practice, results are so-so . Unless you have a 100 gallon tank spraying alcohol/water and ice or liquid nitrogen, the benefits are minimal at best. But, if you have extra time, it’s worth a try.