even after it has "broken in" your RO unit will seem painfully slow.. drip drip drip.. and you will notice that it discharges A LOT more waste than usable water, unfortunately..
that's just the nature of the beast. This is where a reservoir comes in handy. Make up like 100g at a time. Turn off RO unit. Use up the 100g then make more.
Not sure if yours has an auto-shutoff or not but if it does I would not rely on it 100% of the time as it will likely reduce the life of your membrane. Instead, as suggested above, make up a batch then completely shut off the feed water to the whole unit while not in use.