Here's some additional ideas:
A bone simple roof washer, so you don't have to drink water with dead bugs in it like you do now. (Did I tell you what I remove when I fill the tank down at the fire station?)
This is an underground tank that costs $1400 dollars.It holds 1700 gallons. Various others are available.
Got to go. I'm being hollered at about fenceposts from the garden, and have to go see what I can do to help.