You have a leak some place. Either at the foot valve or check valve, or in the water line. If the leak is in the well, the water will just run back down. If the leak is in the wall, it will cause damage. If the leak is at a faucet, it goes down your drain. It depends where you are losing pressure, as to what damages it is causing. One thing for sure, you electrical bill is going to be higher with the pump running more often. Leaks never repair themselves. You should get it fixed.

I did some checking. Closed valve to sprinkler system, continued with slow drop in pressure. Closed the main water valve to house, still slow drop. So, I guess the source of the leak is the well? Since it is a slow leak, will I make anything worse (other than more frequent pump use) by not fixing it right away? The well is about 33 years old. Is this a factor? I have noticed more crud when I change the filter in the house. Pulling the pump is a 3-4000$ job and don't have the money now and even wonder if I should dump that much money in the well again considering its age.
Thanks for your help!!

Although the line running into the house could be leaking, it's quite possible the system is draining back as Pelican described. It's possible, after that many years, that a buildup has accumulated on the check valve especially since you've noticed more crud and it is not totally closing, allowing some slow back flow. I don't want to throw a worst case scenario fear at you but, if you are noticing more crud, the line to the house could have a leak. The vacuum of the water returning to the well could be sucking some dirt in and then into your pressure tank when the pump pushes water back up. If you have a check valve near the pressure tank, try cleaning or replacing that. If you do it yourself, a new valve runs about $35.00, some pipe dope or Teflon tape and the job shouldn't even cost 50 bucks.

You can open the well cap and listen. You can sometimes hear the water falling back. Do you get a sputtering noise when using the water, as if air is coming out?

If there is a hole in the buried line to the house, you'll keep pumping dirt and air into the pressure tank and could pull some dirt back into the well. I hope that is not your problem but I would suggest you find the source of the problem now just in case. It's a real headache for you and the plumber if done in the middle of winter.

"It's a real headache for you and the plumber if done in the middle of winter."

Don't ask me how I know this is true! For me, this would be motivation enough to deal with it one way or 'tuther.

Thanks for all your input! No sputtering or air when water is turned on. The filter is dark gray and smelly and needs to be changed once a month. There is some sediment in the bucket after changing the filter but there always has been. We also have what looks like metal particles in our outside water which tends to plug up the sprinkler heads. Always have had that too but it is getting worse. Our neighbor just drilled a new well because he was sucking up sand. Most wells in our neighborhood 30-40 years old. If the system is "draining back" can I let that go on for a while without causing more problems? If it is the pipe from the well to the house (which runs under the garage) do I call a plumber or a well man??

a good plumber should be able to diagnose your problem. Pulling the pump should not cost 3-4k dollars. Maybe if done by hand, but with these new pump pulling carts it should take a half hour and cost no more than 600 dollars, not including any nedded repairs.

I have had this problem happen to me twice. The first time was really odd. For a few mornings when I walked our dogs by our well shortly after I moved into the house, I heard a slight rumbling sound from the well head area. But it was very muffled. After a while I investigated. The area around the well was landscaped with bark dust laid over black plastic. The connection between the well head and the PVC line that ran to the house had developed a tiny crack. A needle-thin stream of water was shooting out and eventually bored a hole through three feet of dirt but was blocked by the black plastic (which caused the rumbling sound I heard). Easily fixed.

The second time I noticed the problem because the well kept cycling and eventually I began to lose water pressure. So I dug up the well head figuring the same thing had happened. No luck. So I dug at the other end where the PVC line comes into the house (thank god the prior owner left me detailed drawings of the plumbing layout). This was a real pain since the line was about 4 feet underground and the loss in water pressure occurred when it was about 35 degrees outside and raining. I dug down and eventually got to a giant muddy mess where the PVC line connected to a copper line. The fitting was cracked. My guess is that in both cases the builder wasn't terribly carefully in ensuring that the PVC was placed on very solid soil in the trench near the connections to the well and house.

I am stumped now. The pump cycling with no water usage stopped on its own. Lasted for about a week. Then pump started going on again about every 1 1/2 hours for about a day. Now it has stopped again. Pressure is holding steady. Could a valve leak of and on? Any one have any ideas??