Rain Water Quality On Old Vs New Roofs
Project: I ran water quality tests on rain hitting an old roof vs a new roof.
If you're collecting rain water in rain barrels for use with your trees or garden, how does the water quality change if you have an old roof vs a new roof?
I bought two water quality tests and ran them on water I collected from an old roof and a new roof. The old roof is 20 year old asphalt shingles. It's "builder grade" - i.e. the lowest quality, and definitely at end-of-life.
The new roof is a brand new, high quality "architectural" asphalt shingle, one of the top of the line. But still asphalt.
Collection Method
I waited until 1 week after the first rains of spring, to let the initial rain water wash off residual gunk left over from winter. Then I emptied the rain barrel and drained all of the water inside. After the next rain I collected water from the barrel, and ran the test.
Using The Kit
Using the kit itself was quite easy. It gives you a dozen test strips to dip into water samples and then a set of colours to compare them. It's handy to have a stopwatch or timer running so you can count some of the timing - some samples need to sit in water for 5 - 30 seconds before you check the colour. As a first time user it took me about half an hour to go through all of the steps.
Results
Here you can see a chart of the results on the old roof vs the new roof:
Overall analysis: about the same. Boring!
Well I have to say that's not the exciting result I was looking for. But it's good to know that collecting water from an old roof and a new roof might be roughly the same. Several of the categories were better in a minor way.
I was disappointed that the Total Dissolved Solids did not go down with the new roof; that's the one area I thought would improve, if you have less 'old shingle gunk' washing off your roof and into the rain barrels. But it’s good to know if asphalt shingles just always wash gunk into your rain barrel water, no matter how fancy, high-quality, or new they are.
It's sad to see that e-coli are present in both readings. But you probably have birds sitting and pooping on the roof no matter what.
For a third test I was going to collect water from a metal roof and compare that as well, but with the results here being mostly zero I'm not sure it would show anything different. Hopefully you get lower TDS from a metal roof.
So at least now I know. If you ever do a similar experiment I'd love to hear about it.