Disused water well

How deep is the well, if swallow a garden pump and generator maybe.

Then the first thing to do is measure how deep it is and at the same time measure the depth of water.

Just use a bit of common sense. Take your time and don't put anything down you don't mind losing as you don't know what's in the bottom that might trap something but on the other hand try not to loose anything yourself down the well that might later mess up a pump.

I was going to go to a long explanations but google found me this that has all you need to know to get started https://inspectapedia.com/water/Well_Depth.php

Basically all you need are a suitable length of line a fishing float and a weight. The weight and line to find the total depth and the float to find where the surface of the water is. For the surface you need a weight under the float to weigh the line down but obviously not heavy enough to sink the float.

Fishing line is quite good to use as you can easily feel when it goes slack. Builders line is another possible which is similar to what you'd have on a clean fence reel. If you have any problems finding the water level then another option described in the link is water finding paste. Its used to see if there is water in the bottom of a fuel tank but smeared on the bottom part of the line will show up what part of the line went in the water with just a weight on the line.

Think the first thing is to start looking around for a suitable pump for the depth of the well. Once you have that I'd see if I could pump the well dry then see how long it takes to recover (fill up again). I've only done this with old shallow wells but its the same for deep ones. You only know how much you can get if you pump it nearly out. If you are down in an aquifer then you may not pump it dry. Its a common sense balance. If you need X amount of water in a day and you can pump that in a couple of hours and you are still pumping then no point on keeping on forever. Knowing the depth of water to start with is fairly critical because you don't want the pump sitting on the bottom sucking up sediment. Hard to say what depth to put the pump at but I'd start with it half way into the water (say you have 20ft of water then put bottom of pump 10ft into the water) and you can monitor the water coming out at different depths as you lower it foot at a time.

I would try and pump the well as low as long as possible at least a couple of times just to get the well flowing again. If you pump the water level down low then in theory water can push its way more easily into the well. As it does that it hopefully will bring any sediment that is slowing the flow down. So the more you pump the faster the water can flow - but of course if its a poor well it might hardly recover at all. It just depends on where the water is coming from and what the well is drilled into.

Ideally you are looking for a balance in the amount of water you can draw relative to the depth the pump is in the well, the power of the pump (how fast it can pump) what the well can continuously supply and the amount you need. You may be able to get loads of water quickly with pump nearly on the bottom of the well but also get loads of sediment coming up. On the other hand you may constantly get just a few liters a minute of clean clean water from having the pump higher up. Obviously the higher the pump is in the well the less water there is for it to pump before it runs out.

If you can keep measuring the level of the water you can see how quickly it goes down but most people I'm fairly sure don't bother and just heave a pump down to the bottom lift it up a bit and off they go, it either works or they spend a lot of time cursing it.