I don’t understand the recent fascination with rain barrels. For the not so informed, the idea is that the rain from your roof runs down into your gutters, and then your gutter runs into a barrel. Now you have all of this water. But what are you supposed to do with the water? Water from your roof is not clean water, its got chemicals from your roof shingles, plus little bits of bird feathers, squirrel fur, and whatever else has been up on your roof.
Obviously you couldn’t drink this water (if you value your life anyway) nor could you use it to water your vegetables (for the same reason). So what are you going to do with it? Water your lawn? You will need a pump and a hose. Water some flowers? Again, you will need a pump (or a watering can I guess). You can’t give it to your animals. So what’s the point? You aren’t being green if you can’t use the water. Maybe you are trying to increase the mosquito population. I don’t know. It just seems to me that resources could better be spent making something worth while that you could use, than wasting it all on a giant plastic barrel.
Straight up, next level bullshit. 
Josh:
There is a very important aspect to rain water retention that you have overlooked. The term is storm surg – IF everyone were to retain a bit of water from an impervious surface and then release it on a dry day (when the water table can absorb it) then you will reduce the impact on the environment and on the water treatment plants. It has been proven that if more folks did this then there would be a dramatic reduction in flooding.
I’m not trying to take away any business from anyone selling these things, but I don’t see this as a realistic solution. Lets look at this from a purely mathematical standpoint. Assume we have an area that is one square mile (approx 640 acres) and we say its all homes and that all the homes are on a quarter acre of land. So we have 640 x 4 homes (lets ignore roads and everything else that would also block rain water from seeping into the ground. So that’s 2560 homes. If it rains one inch that is the same as (according to the US geological survey) 17,378,560 gallons of water. Lets say that half of that water seeps into the ground, giving us an excess of 8,689,280 gallons of water that would need to be stored. If we divide that amount of water by the number of homes in our 1 square mile, each household would need to store 3394 gallons of water. That is a retarded amount of water.
So now lets change this up a little, lets say at 90% of our one inch of water seeps into the ground in our 1sq mile area. Now we only have to deal with 10% of our one inch of rain, which is 1,737,856 gallons of water. Divide this by the number of homes and you get 678.85 gallons each household would have to store.
Lets go farther, lets say that 99% of the 1 inch of rain seeps into the ground leaving only 173,785.6 gallons of water we need to deal with. Each homeowner would need to store 67.885 gallons of water. What does it cost to store this much water? Almost $300. But keep in mind we have excluded roads, parking lots, and business, which would cut down on the overall number of homes in this area.