Question
I have an old concrete cistern (probably used as a well some 70+ years ago).  It has been left unused, blocked by a concrete slab for over 40 years. What would it take to make use of this for irrigation purposes?  Ideally, I would like to collect the water that drains down from my roof/gutters into the cistern, then pump it out to the lawn and garden.  Again where do I start?

Answer
You will need to install a pump system and then connect it to your existing irrigation system.  But I would also keep in mind that irrigating uses a lot of water, so unless this is a very large cistern, or the water is replenished in it contiuously, it may not be worth the cost of installing a pump and the related equipment.  

Check out this website for a good tutorial on using a pump:

http://www.irrigationtutorials.com/pump.htm