Spring box... cistern... well???

I'm new here so please be patient with me.
I recently purchased 5 raw acres. On the property I was told there was an artesian well. Upon clearing brush, grass, etc. I discovered 3 concrete casings which are located in a wet area of the property. Each of which are 3' across. Approximately 10' deep (I'm unsure as to the actual depth due to sediment). They are also connected at some point. Water level was approximately 8 ft.
1 tank had what appeared to be clean & clear water. The other 2 were tainted due to the concrete covers being slightly ajar allowing bugs & critters in.
1 tank had at some point been plumbed but is long gone to history.
I drained the roughly 1500 gallons and am now waiting to see the recovery rate.
So I ask... What do I have? What should I do to properly clean these cylinders?
I'm hoping once done I'll have potable water.
Thank You in advance.

Are these concrete casings in a low area?

The ground is all relatively flat but this particular spot is a tad lower.

My guess is that it is a cistern to catch rain water from the land.