Over the last week we have noticed a significant decrease in pressure in the washing machine, one bathroom sink and a different bathroom shower. To address this I removed and cleaned the filters. They were filled with a yellow sandy gritty substance. This resolved the problem and everything was fine. However, within a couple of days the same problem recurred.

Any ideas on the source of this gritty substance? Why would it only be affecting a few of the faucets?

Thanks

By the way it only happens in the cold water inlet on the washing machine.

Are you on a private well or city water?

City water into water softener through copper piping

I'm not an expert so don't put a lot of stock in my answer.

My guess is your having water softener problems. I don't have any experience with them so I don't know the required maintenance. As for only affecting the cold water, the hot water heater could be acting as a trap. I would bet that if you flush the hot water heater you would find that a lot of this debri (rust more than likely) has accumulated at the bottom of the tank.

How old is the water softener? You said you cleaned the "filters" Did you mean the aerator at each faucet? If so install line filter prior to water softener. The debri could be from water main.