Why does my water pressure / flow rate drop sporadically?

Question

This is a recent problem that I've noticed since Hurricane Harvey came through a couple months ago. No flooding in the house, but there was 1-2' of water on the street, which did cover the water meter and shutoff (and a couple in-ground irrigation heads) for ~2 days. I'm on city water (i.e., no well, which makes this similar question not a duplicate)

Some time after a water fixture is turned on, the pressure and flow rate will drop for a second or two and then return to normal. It will do this repeatedly, at different intervals. Nothing regular that I can tell. It's like when you have a faucet on, and then turn on the outside hose or sprinkler - that kind of a drop. But it returns quickly, only to do it again some amount of time later.

Sometimes, I'll be able to use the fixture without it experiencing this drop in pressure / flow at all, or I'll only experience one or two drops. Other times, it happens every 30-60 seconds. It happens on all sinks, the master shower, and upstairs tub. Don't know about dishwasher and washing machine. I've experienced it on the outside hose bibs as well.

What could be causing this and how can I fix it?

Answer 1

I guess you did ask how to fix as well as why, so this does answer that half (formerly a comment, I don't know why, other than probably city supply issues.)

You could mitigate the problem (if it annoys you adequately) by putting a pressure tank (you can call it an expansion tank, but in the market those are usually small and I'm suggesting a larger one) on your side of the supply, after any Pressure Reducing Valve (PRV)/Regulator (add a check valve if you do not have a PRV/Regulator.)

Set the empty tank pressure 10 PSI under your normal pressure, which should give you a buffer of water & some allowance for the occasional pressure spike as well - if you have a PRV/Regulator and don't see much for pressure spikes, you could set the empty tank bladder pressure 15-17 PSI below your set pressure to have more of a buffer. When input pressure drops, the air pressure in the tank bladder will supply water to your stuff, while the check valve or PRV/Regulator acting as a check valve will keep it from trying to hold up the city pressure. When the city pressure returns, it will refill.

Answer 2

Probably city pressure not yours many stations were affected and others are pulling up the slack. There are some MUD's that are running 50% due to pump lose. If it happens at peak usage times then probably that.