[Motor31]

Some filter packages state the water flow rate the filter will support. In the case of the filter I listed from wallyworld it is rated at 5 GPM, same as the plumbing in our rigs, with the exception of the low flow fixtures. If you get a filter with a 2 GPM flow rate you will have full pressure at the fixture only when the tap is closed. As soon as you open the valve the water pressure will drop as the filter can't flow enough water to maintain a pressure stream. The smaller the filter pores are and or the more dense the filter media is the less flow, particularly at 40 PSI. This is the same siituation you get when the filter gets clogged through use.

Flow rate is the reason those little cheap inline water pressure regulators cause the flow to drop so dramaitcally in our rigs. They do reduce the pressure but they also reduce the flow so much you don't get a decent flow from the tap or in the shower. A residential style regulator will reduce the pressure and allow a good flow rate of water with the tap open. The RV filter store has a great regulator or you can go to a hardware store and put together the same kind of regulator assembly (regulator plus hose fittings) yourself. The cost is about the same depending on where you go.