Identify your State and match the color up with the chart below. Always use the high figure. If you happen to be in a extremely hard water area of 14 gpg or higher use the figure 20 gpg. to size your system. Our systems will remove up to 150 GPG of hardness at a time so your water will be Soft regardless. The sizing of the Water Softener is for the purpose of not regenerating as often saving you money on salt / potassium and has nothing to do with the performance of the system.