I used to live in Colorado, and at one time owned a house with a well.
Re: wells, find out everything you can about that well, including the type of permit it has. From what I recall, there are various types of well permits that dictate what the water can be used for. For example, some permits might be for household only use, or for limited livestock watering, etc. Even though it's a 40 acre parcel and you could have horses and other livestock, the well permit might restrict what you can use the water for.
Also, regardless of the type of permit, make sure you, as the buyer, have your own independent tests done for purity and production. At the time I bought my house in Colorado, it was common for the seller to have any septic systems inspected and/or pumped, but it was the buyer's responsibility to have the well checked for anything they were interested in.
You want to make sure you know the well's production (gallons per minute) and static level (how many gallons it holds without pumping). When I had the well tested of the house I ended up buying, I remember the well drilling company I hired to do the inspection hooked some equipment up and tried to pump it dry for like 30 minutes so they could get readings on both production and static level. My well ended up being fine for both, but I can't remember the numbers. If you have a well tested, make sure you go with a good reputable well drilling company in the area, who is aware of things like the local water conditions, aquifer, etc.
I ran across this diagram that shows a well layout, that might be of use:
http://mbmggwic.mtech.edu/sqlserver/v11/help/welldesign.asp
To test purity, I remember taking some samples of the water and having them sent off to some lab for tests, and they sent back the results. It was a little heavy in some minerals, but nothing out of the ordinary with wells, so it was fine.
If you pursue tests of this kind, make sure you account for the time required to do them in your inspection timeframes in the contract. You want to make sure you have enough time to complete all your inspections like this by the deadline in the contract, so that if anything looks bad, you have a chance to get out of the contract.
Good luck with your pursuit of the property! Can't wait to get back to Colorado myself hopefully next year.
EDIT: Forgot to mention...one other thing to look for when researching the well permit is to try and find out if the well ever had to be drilled deeper in the past, which could include the water level dropped, it ran dry, and had to be drilled deeper. Or, if there was a well somewhere else on the property that went dry and they abandoned it, capped it off, and had to dig a new well. All that kind of info will be important to know in making your decision about the viability of the well. I remember the well driller I used telling me one thing a lot of people don't think of is the deeper the well, the more expensive it is for the pump and cable, because the deeper it is, the more powerful a pump they have to put in it, and I guess the power cable to it has to be bigger (or something like that). Anyway, possibly useful info, so thought I'd throw it in.