Rooftop Catchment

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Credits: Dan the Irreverend

Download higher resolution PDF: File:Roofcatch.pdf

Download rooftop catchment potential spreadsheet: File:Catchment.xls


  • Get cheapest washed gravel - small works better
  • Porosity of pea gravel is .65
  • Dan puts liner (check in the cistern, then rock, then culverts, fills it up.
    • Need to find sourcing information for liner
    • Need closing detail for seams and around culverts
  • Gallon/day/person - 15 gal/day bath-cooking-water-animals
  • 3-1 long to wide
  • 2x depth away from house
  • dig a ditch next to gravel tank - put side and top liner there - roll a piece of PVC, screw down to keep anything from getting in there.
  • Culvert with pie cuts
  • Culvert looks like a riser. Riser comes out of ground 6" - so no flood water.
  • Go down to 1 micron - 500 gallon tank
  • Reef Industries - 19 mil - should be about 30 cents per square foot.
  • pressure-compensated septic drip tubing at Home Depot


Gravel Types

  • Type of gravel to use:

  • Gravel - Marcin, it looked to me like this was cracked rock, fractured and highly faced?

What you need is what they use in concrete so go to a concrete plant--unless that was what they use for ballast in their concrete. The guy is right, the smaller the pebble the larger the entire void space (more water) you can hold in that stuff. The absolute way to check it is to fill a bucket or two with different materials and then add water, then dump and measure the water. Ideally you want 3/8 to 1/2 inch pea gravel, not cracked limestone or chirt. But, in the end you use what you can afford! The guy also was right about the critical mater of clean. Fill a bucket with the selected materials. Fill it up with a hose. Slosh it around and dump out the wet stuff. If you get a full cup of dirt and "fines" like sand, okay, but more than that you will pay for water loss you cannot see when they dump it. Small, round, and very clean is the stuff you really need! That's from Goethe and me!

Cistern Detail

You buy the best liner you can afford--just use old carpet behind it to keep it from rubbing while putting in rocks etc. 10,000 is not a big tank, so medium grade is all you need. You can buy huge tanks but they are over $5 a gal installed and will pop out when empty...not a dyi project. You might look into a heavy swimming pool liner--my 18,000 pool liner cost me $145 bucks and it was the medium grade. Just email In the your tank measurements and get a quote for their best liner--it will do! I'd put blue board 2inches on the bottom taped together at seams and at least 1 inch on sides then liner and then nylon carpet on the bottom before you dump in rock and then just let the rocks slide down into the corners from a central pyramid/cone. You can shield the sides with 1/2 in plywood or OSB as the rock hits the liner and then gently slide the wood up to let the rock settle gently. If you have the money for materials and not the time or labor just line the entire pool with another thin layer of blue board INSIDE and over the liner and then just dump away.

On sealing around culvert - cut the sheet pulled over the culvert into slices of pie. Slip it down over the culvert and then loosely fit a nylon luggage strap with pulley tightener and use that to seal the liner. I'd slop some good caulk in there after I got the strap sorta in place. Once you bury it it can be sealed better with cement but it won't matter if it leaks some.

Carpet is contaminated but so is dirt--full of shit and bacteria--your water is coming from a seriously contaminated/toxic roof--who gives a shit about carpet if it keeps you liner from tearing.You have a plan to disinfect and treat the water out of this cistern, I'm sure.

Get some help designing a proper ozone system from Aquatic Eco. I'd pay for some professional consulting on the clean water issue.