Indoor grow help

First off, what is a ballast, and second I just need a good site to order everything from

http://cgi.ebay.com/SWITCHABLE-HPS-METAL-HALIDE-400-watt-Grow-Light-w-mh_W0QQitemZ270604179199QQcategoryZ42225QQcmdZViewItemQQ_trksidZp4340.m263QQ_trkparmsZalgo%3DSIC%26its%3DI%252BC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D10%26pmod%3D270663192786%26ps%3D63%26clkid%3D7462024560073945141 here you go

The ballast provides electrical current to the lights. Lights require a high electric current to turn on, but after they're one the electric resistance drops and the light requires less current to maintain it. A ballast takes electricity and passes it to the light at high current to start it then switches to the lower current to sustain it. You must have a ballast to limit the current after the light has turned on, or else the bulb will have high current with low resistance and blow up. There are multiple types of ballasts, and they are specific to the type of bulb you are using (although there are some that can switch between types)

question here for me as well... do i let tap water sit out for 24 hours in a big resouvuir, since i change the water i my 5 gallon buckets manually?