I'd suggest a unit with a 75 gpd membrane. The cost will be hardly different from a unit with a lower gpd rating, but the rejection rate of the 75 gpd membranes is better than a 100 gpd membrane. Besides, the ratings are under ideal incoming water temp and pressure conditions. It's a struggle for many of us to always acheive those conditions, and a 10F or 10psi change in the incoming water can have a significant impact on the production rate. It's bad enough waiting almost 2 hours to make 5 g of water -- couldn't imagine waiting 5 or more hours to make 5 g with a 24 gpd membrane.