Rain Harvesting???

Promethean made the very good point that you have rainwater only when you don't need it.  You need something to last the off season.  I don't see the point in storing anything less than a 2,600 gallon tank of water, and even that gets used up pretty quickly.  A 55-gallon drum might be good for livestock in the winter, but at a certain point it is not worth the effort because it is gone a few days after the rain, max.   Getting a pond liner and making yourself a proper little retention pond might be the most economical way to go.  The heavy plastic tanks get expensive. 

I am looking ahead to what might be a VERY dry summer season here on the NorCoast, and rigging up more rainwater storage. 

BTW, I personally make a huge distinction between downspout runoff and gray-water sudsy dishwater.   I hear you have to expect a pretty nasty tank with the true gray water. 

   Update:

  Last Sunday I decided to take 1 of the 5 55 gal drums I have and set it up under my gutter system down spout.  After acquiring all the stuff for the inlet & overflow, I leveled the space for the drum, removed sections of the downspout and redirected the water flow into the drum. 
  Monday afternoon when I got home I checked on the drum by trying to move it, thinking there was going to some water in it, but it was full!  The rain we had was never really heavy that night, I guess just a constant drizzle/fog.  Anyhow it was enough to fill the drum.
  I have 4 more (Will have 8 total) that I need to plumb up (Series/parallel, side-by-side)  after leveling the site where I plan to put them.

 
 

 

Update II

  Just found a slightly weathered but never used 500 gal tank for cheap!  No holes in it either!  I located the property owner, and talked with him about what his plans were for the tank, he said he was going to get rid of it. 
That's where I come in!   paid for it, then went to see if it would fit under my campershell. 
It had about 100 gallons and about 1" of mud in it so I was not able to tip it over in an attempt to slide in it the bed.  Used my winch to pull the tank over and then began to bail the water out.  1/2hr later it was empty enough for me to tip it the rest of the way over to drain it fully.
  Cool, now it's time to try and load it in.  DOH>>>>  won't fit.  Hit' the campershell window!
Darn.  Maybe I can raise the campershell up prop it up and slide the tank in then strap the back down.  I measure the tanks diameter with a kayak strap, and then take that measurement and measure inside the campershell.  about 3" too short! 
  A call to the local Home Depot to see if they have a rental truck available and they did!  Off I went to get it!  A Ford F350 (Gas hawg) go get it, return to the tank toss it in the back,strap it down, and head home.  The alternative plan was to leave the tank till Saturday, head to my friends house and remove the campershell, (2 people minimum) then go get the tank drop it off at home then go put shell back on.  Truck rental seemed much easier.
  Saturday morning, I rinsed out the mud then moved the tank down into my yard.  Sunday, Wife & I (She decided I listened) on a nice spot, exactly where I put the 1st 55 gal drum.  I'll have a lot less work at that location then where she was originally thinking about putting it. 
  So, I get to dig out a little bit,to help level out the spot, then build a small retaining wall 54" square to build up the slope to level,( about 18" tall at bottom of slope) add base then cement me a small pad for it! Running the water to it will be super easy!  Won't have to do anything to existing gutters! Just shorten the down spout!
  Next rainy season we'll be set for a little while into the summer. I have a few pictures, just not removed from camera yet.