Harvesting Rainwater

Hello,

I want to disconnect my downspouts to collect rainwater and eventually use the water in my food garden. Does anyone know if I need to be concerned about the water picking up harmful chemicals from roofing materials?

I'm thinking of making a rain barrel for storage out of a plastic garbage can I have. Do I need to be concerned about the water picking up chemicals from the plastic if I'm using the water on food plants?

Thanks for any help you can provide,

Rob

When we put our rain water collection system in the consensus was that you can only take water off the roof because it is clean and that it doesn't spend long enough in contact with the roofing materials to pick up anything bad. Maybe it's like the 5 second rule Since we haven't tested I don't know if this is actually true.

some say not to use the first X amount of gallons of water to flush out any impurities from the roofing material.  me personally i dont worry about it to much.

Dead Rabbit wrote:
some say not to use the first X amount of gallons of water to flush out any impurities from the roofing material. 

I think that's mainly if you're going to drink it.

Plastic corrugated roofing and metal are ideal for water catchment.

The most widely used(in my neighborhood anyways) is composite roofing. Theses tend to, this water release chemicals that would not be ideal for water in edible plants or drinking water. As for plants that you would not be consuming, it would be okay to use the water for these.

So assume you probably don't live in Hawaii, but this will be informative either way.
http://www.ctahr.hawaii.edu/oc/freepubs/pdf/rm-12.pdf

On the Big Island of Hawaii, almost everyone uses water catchment system. It is such a great way to conserve water.

Asphalt tiles are a no-no for drinking water.  They are questionable for edible plants.
The biggest limitation to water catchment is storage capacity.  Gardening books claim that you need 1" of water per week for most gardens.  At that rate, a 55 gallon barrel will only supply enough water to water a 35 square foot garden once.

One inch of water on an acre equals 27,152 gallons.  That's almost 500 barrels.

When I get our house tank plumbed, we'll have 11,000 gallons rainwater storage.  But still the most efficient place to store water is in the soil, especially water for plants. 

http://www.harvestingrainwater.com/

I should mention only two of the tanks are plumbed to metal roofs - the others are composite (contain asphalt).  I feel a good active organic soil should be able to handle the small amount of petroleum products and other crud.  But I would not drink the water except in an emergency.

H Ludi Tyler wrote:
I should mention only two of the tanks are plumbed to metal roofs - the others are composite (contain asphalt).  I feel a good active organic soil should be able to handle the small amount of petroleum products and other crud.  But I would not drink the water except in an emergency.

i agree.  my system if for garden and tree watering.  non potable water.

I've started with a couple of 55g barrels 'in series' off a tiny roof.
Don't underestimate the amount of water you'll get!
I think sorting out what to do with overflow's about the most important consideration.
I've got free-draining, sandy soil and my overflow hose just gets moved around the place. Heavy soil and winter rains could be a problem to be solved if overflow isn't being directed down stormwater drains.

If you want to calculate how much water you'll collect:

Divide square feet of roof by 1.6
The number you get will be the number of gallons each inch of rain will produce.

Example:  10' x 16' hen house = 160 sq.ft. divided by 1.6 = 100 gallons per inch of rain.

You will get slightly less due to first flush, splatter off, and evaporation, plus whatever your roof may absorb.  Makes it kind of silly to be carrying buckets of water to your hens.