Some people use water and butter at the same time along with cannabis and heat. This is done for one of two reasons IMHO. If you want to use a large quanity of cannabis (as you would if using brick weed), and/or if you don't want to let it get above 212F (the boiling point of water). When finished with the extraction, strain (filter) out the cannabis. Pour butter/water mixture into a container and place in cold refer or freezer. The next day the water will have separated from the budder. Discard water (it will be dirty/ugly). Budder should be green if you done an extraction worth using.
The other way is double boiler (or crock pot, etc.) Break-up bud by hand or use sugar trim, stir into melted butter (unsalted) and heat. Do not pulverize material, use coffee grinder etc, unless you want alot of fines in your budder. This method tastes better IMHO, but will not work well for brick weed unless you keep using the same budder for multiple extractions ( this could take days).