(Flowmaster-3/8) Flow Master 2 GPM Water Flow Meter; 3/8" QC

Instructions state not to install the meter on the feed or after the RO membrane.Thus, the flow-meter should only be installed between filters, and before the RO membrane. Thus the only remaining location to install the meter is between the RO pre-filter and RO membrane.IMHO, this severely limits the practical installation for most prebuilt RO systems.Furthermore, only being able to install the meter before the RO membrane eliminates the ability to specifically meter the drinking water, because drinking water is only available after the RO membrane.Not Recommended for prebuilt RO systems.

You must have a decent flow rate in order for this to read out your water usage. I have a garden drip system that won't use a lot of water at once/ rather it slowly drips out over a full days period.