I am trying to regulate the gpm on my shower head. I was browsing stores and manufacturers online and came across shower filters. If the shower filter regulates the water at 2.5 gpm, and a shower head advertises that it reduces the water flow to 8 gpm, are these items the same? In other words, is the water filter regulating the water more efficiently or using less water than the head? Or are these two items talking about two different types of output?

The shower head will put your flow at 8 gpm, not so efficient. Adding the filter would restrict the flow to a more conservative 2.5 gpm. I would go a step further and add a shutoff behind the shower head. With this little guy, you get yourself wet then shut off the flow long enough to soap and scrub up, then turn it back on to rinse. These are available at Lowe's and Home Depot, sometimes at WalMart and Kmart. If you take 5 minutes to soap & scrub, you've saved 12.5 gallons of water.. times how many showers in a year?