A Brita filter would probably be better than straight up tap water, because it removes certain chemicals. It can't replace an RO/DI filter, which removes practically everything so you are left with close to 0 total dissolved solids (TDS). An RO/DI unit will be incredibly helpful in the future when it comes to keeping your tank free of nuisance algae and maintaining good water quality. You can find good portable units on eBay for as low as $60.