I use two water filters, the on board, and an exterior unit. Change the filters twice a season (may be overkill).
As far as the hot water annode I change mine at the start of each season, and flush the tank at least twice during the season. The cost of a new annode, $20., is a small price for the insurance.
2012 Georgetown XL 360
2011 Chevy Equinox - 2006 Chevy Avalanche