GPM is the amount of water the shower head uses.
For example: A 1.5 GPM shower head uses 1.5 gallons of water per minute.

High Sierra® offers 5 satisfying flow rates:

1.25 GPM – For those wanting the maximum amount of water savings. Usually recommended for handhelds or applications where the spray is close to your body. The majority of our customers do not choose this flow rate for standard fixed shower head installations.

1.5 GPM – For those wanting to maximize water and energy savings without having to sacrifice performance. Consistently rated as equal or better than 2.5 GPM conventional shower heads. Our #1 selling flow rate.

1.8 GPM – Uses a little more water than the 1.5 GPM models but produces even larger droplets. Superior rinsing capability makes this flow rate ideal for those with extremely thick hair. Especially recommended for shower arms over 6.5′.

2.0 GPM – Uses more water than all of our other flow rates but is still considered a water conservation shower head. The exceptionally large and heavy droplets are reminiscent of shower head performance predating government mandates. Especially recommended for shower arms over 6.5′ or ceiling mounts.

2.5 GPM – Established by the Federal Government in 1992 as the maximum flow rate per shower head allowed in the USA. Today, the federal mandate continues; however, 2.5 gpm is no longer considered to be “low flow”.