I've used my grey water system for about a year now. I have two grey tanks and use only bathwater to flush the toilet. The setup uses a pump, filter, a few valves and pex tubing. I gain about two extra days of water use and when I'm out of fresh water my waste tanks are half full. I also have a 55 gal plastic drum with a demand pump mounted on it. When that is depleted my waste tanks are all full. All told I'm usually good for at least a week without conserving. Cost for the grey water system and extra fresh tank and pump is less then the cost of "your" system.