Why is the water pressure in my shower getting steadily worse?

Sounds like you might have a leak somewhere in the system?

Try removing the valve stem from the on/off valve. Could have some sediment in there. Not difficult to do. You can google the manufacturer and get a schematic if you need to. Turn off the water first of course!

Test the water pressure at the lowest point of the house. If you have a laundry tub in the basement, this is a good spot. If your overall water pressure is good, then you have a blockage elsewhere in the system, most likely in the shutoff valve for the shower. Does the shower feed from a diverter on the tub spout, or does it have a dedicated valve? Diverters don’t always seal well.

There is rock in the water. Over time it will clog the holes that the water comes out of in your shower head and will eventually clog your pipes and ruin your hot water heater.
A good water softening system will take care of that.

If that is the problem.

See @Cruiser You start going back down the line. If it is not the shower head, check the valve. If not the valve check the hot water heater for deposits. If it is not that, check and make sure the house hook up to the external main has not failed. Also, the more houses that get plugged into the system, the lower the pressure.

Do you have a household water filter? We lived in our house for 3 years before we found out we had one, and found it by losing pressure (filter was clogged up). Or if you have a well (like we do), maybe the pressure pump is going out? (That’s what we thought was happening, called the plumber, and he found the filter.) We’re good with computers, not so good with household stuff.

Wow, thanks all. I think I now need Plumbing 101. @Cruiser and @josie, where does one find the valve stem and the on/off valve? The shower does not feed from a diverter on the tub spout, so that’s not it. Our overall water pressure in the rest of the house is good, so the valve seems like a good theory. @llewis, we don’t have a well. I don’t believe we have a household water filter, but I’m not sure where to check. @josie, how/where in the hot water heater does one look for deposits?

It would be so awesome if we could fix this ourselves and not call a plumber…

@sarahsugs It will be a lever that you turn or a big button that you pull on to turn on the water. It will be in the middle of a decorative metal plate about the size of a desert plate. If it is a lever, there will probably be an allen set screw at the base that you have to loosen. If it is the big button, usually a decorative plastic logo disc is on the front of this and it can be pried off carefully. A screw will be underneath the logo disc. This holds the button on. Remove handle or button. Remove decorative wall plate. What you are looking for is attached to the water pipes in the wall. Make sure household water main valve is shut off and open a downstairs faucet to drain out the water in the system before you replace the mixing valve.