I received a couple of inquiries about the rainwater harvesting set up and the large container. First let me thank Joy for the link and sending some of you here. Click here, to visit her.
N's rainwater harvesting set up is very low tech. They simply catch the water in buckets under the drip line of a gardening shed. We dip our watering cans in and take the water to the greenhouse. The large tank is a recycled tank that held some sort of food product, maybe oil. It could be attached to a gutter down spout. N's husband simply uses a sump pump to syphon the water from the buckets into the large tank. I am sure this is more important in the summer as a means of mosquito control. We have not used the large tank at all this winter. There is a hose attached to the large tank. From there, the water is gravity fed through the hose to our plants. There is not much water pressure, but we don't need no stinking water pressure(sorry, the silly had to come out somewhere). Because it is opaque, I have not seen any algae in it so far. If it were clear plastic, it would need to be painted to avoid algae growth.
If you want a more sophisticated system, they are out there for sale. These set ups have a first catch tube to keep the main tank clean, use guttering to collect the water, and often have electric pumps to allow for drip irrigation or soaker hose use. There is also an equation that lets you know how much water you can collect per area of roof and inches of rain. I don't like to do math, but from what I have seen it is always A LARGE AMOUNT OF WATER.
The bucket system works great as do a couple of rain barrels. Hope this helps. If you need more information, I can find it.