I would like to monitor the water depth in  well.  Maximum depth is 500" and minimum is 0'.
I have been thinking pressure sensor but everything I have found is quite expensive packaged sensors.
Any ideas on other ways to monitor depth or sources of something I can use for a sensor in a 500' well.

Mount a pulley wheel above the well. Wrap a couple of turns of rope around it. Suspend something that floats on one end of the rope and something that sinks on the other such that when one is at the top the other is at the bottom. As the float moves up and down with the water level, count the number of turns of the pulley wheel. With the right choice of pulley diameter you could either count the turns with a mechanical or electrical up/down counter or arrange to turn a pointer by using gears driven by the pulley.

1) Unless you are a well, hobbyist, addict (like I might admit to), as VE1BLL correctly points out: caring about the wells performance/recharge rate will be as exciting as watching grass grow or more directly; a puddle evaporate.  You will find out the well performance/capability soon enough and it will be fine or you will need to make changes(no baths on alternate months).

  Frankly if you are running a tank as is required most everywhere, for how else do you provide the 1,500 gallons of fire fighting water most places demand, then it will be no problem to keep that thing full unless a dairy is involved.  You are providing a tank? Tell me you have a tank.  A nice 2,000 gallon one... Or two.. The guy next to me put in two 5,000 tanks side by side to support his private one person observatory bathroom, (the only thing on the site.

2) You can easily see if the pump is going dry by watching the discharge pressure.  I don't care if that pump is made out of pumice spinning in cotton bearings, it's not going to lunch itself in 1.00 seconds while it starts to suck a little air/water mix.  You are being overly paranoid. Yes you would not want it to go on and on nor occur at the end of every pump cycle but a few calibration gurgles is not a problem.  If you are convinced it is a problem then you must buy the $1,115 plus submersible sensor noted above and some electronics and monitor the well performance and turn off the pump too while your at it.

As I continue to beat this horse,(now into a red pulpy goo), Here's-what-I-would-do: :)

1) Put up a storage tank if you don't have one. This drops the panic factor when working on the well as you have a few days of reserve on hand.

2) Put up a storage tank as this is much better for the down hole pump to not cycle constantly.  It also allows a current or flow monitoring if desired.

3) Run the down hole pump with a float switch.

4) Run a second three phase pump with a VFD (single phase input) into a small pressure tank. Use pressure sensor feedback to exactly control this three phase pump to maintain the perfect house pressure. No on/off, on/off, garbage when some faucet-garden hose combination causes maximum pump cycling.

And spend, spend, spend as it's all justifiable. One must have a nice well after all.

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