A typical unit will produce 10–35 gallons of water per day. Now, the typical U.S. family goes through roughly 300 gallons of water per day. However, only 19 percent — 57 gallons — of that is from the faucet (source).
You probably won’t be washing your hands or brushing your teeth with reverse osmosis water. So you can shrink that figure even further. If you use your system for only drinking water and cooking, the water it produces should be more than sufficient.