hot water heaters build up all kinds of crud inside, including mineral and scale deposits.
if you had one of those tankless water heaters, it'd be ok to use that water.
otherwise, cold tap water, just like cooking. because honestly, making beer IS cooking, with fermentation to complete the recipe.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10