also pay attention the the GPD for the rejection rate. Below cut from
here
Difference between the 50, 75, 100 & 150 GPD membranes?
The major difference, besides how much water they can make, is the rejection rate. Normally, the lower the GPD volume, the higher the removal rate is.
The 50 and 75 GPD membranes have about the same rejection rate of 97%. The 100 GPD has about a 90% rejection rate. The 150 GPD membrane is a different story. It allows for high volume without a big drop in the rejection rate. It has about a 97% - 99% rejection rate.