The gpd is what the unit will produce in a 24 hour period. So you can imagine how slow the water is produced. Go with the 100 gpd, it is only slightly higher in cost, and the RO
membrane will last longer than the 50 gpd.
Also invest the $20 in the membrane flushing kit even though it's just a couple of fittings, valve & tubing but this device will extend the life of the membrane by two times.
I ordered the flush kit afterwards & had to figure out how to connect it, if you order it with your RO
, they will probably connect it for you since they are made to order.