Im unable to use tap water here for large water changes at this time of year w/o heating the water first it would drop the water temp in the tank too much.. during the winter its smaller changes but more frequently during the week. Unless your breeding, or if your tank is grossly overstocked, over fed , mismanaged. Water changes are necessary but not at the level I've seen posted on most forums... if your community display tank needs a 50% water change a week to keep your fish healthy you may want to re examine your tank maintenance, feeding routine or stock levels ..however whatever has been working for you stick with it, I prefer to strive for efficiency of my time and costs ? Also note I'm maintaining a basement of tanks not a single, so a 50% water change would be close to 700 gals a week.