And get the biggest you can afford. I have the 125G/day. Although I will very rarely use 125 gallons of RO/DI in a day I can make a 5 gallon bucket of water in an hour. I originally bought the 25 gallon/day filter becaue I thought I would never need more than that in a day..... but it takes 5 hours to make 1 jug full.... you'll be happy you went for the larger version.