Rain-Water Harvesting

History

ASelfcontainedHarvester.doc

5th-Generation Trough

Thursday, January 12, 2023

I rebuilt the 4th-generation trough last summer, using sheet leather as hinges for the two wooden pieces. The Autumn gales shredded the plastic and one piece was found across the street. Of course sheet polythene that is designed to provide a moisture barrier between walls easily degrades in direct sunlight. Brittle, a small piece offered entry to the gales and Whoosh! It was stripped off like a spinnaker in the Sydney-Hobart yacht race.

This will be my fifth generation, and the best so far. See the end of this page for my ideas for the sixth generation.

A week ago I brought the bedraggled trough into the kitchen to dry off and this morning made a new liner.

I am still using polythene sheet, but now a staple gun will fix the three edges along each of the four edges of the trough. And I shall augment the staples with a generous dollop of wood glue.

Picture the sheet lining the trough, then bring the edge of the sheet over the edge of a plank and round to the other side. Stapled at the edge of the trough, stapled along the outside edge of the trough. And stapled again on the underside of the edge of the trough. And where there are stapled, there be glue!

The trough laid out on the kitchen floor. Dark patches show water damage, but the harvested water always ran off a plastic sheet tacked to the timber.

Jagged edges of the old plastic wait to be removed.

I have opened my new sheet of plastic. The sheet comes of a roll that is about three feet wide, but the material is pleated. I needed 10’x5’ so we cut off a chunk ten feet long and, I suppose, about eight feet wide once un-pleated.

I have dragged the sheet so that six inches overlaps one end and adjacent side. The excess will be trimmed away.

Here is a wider view. The side nearest my feet will need to be trimmed to leave a six-inch overlap down that side.

At the far end I have folded the excess. It too will be trimmed off early on.

And here we are, trimmed off, with a six-inch overlap all around.

I will tack the surface along the lines in yellow, then glue and tack the edge and the underside.

I used a short off cut to support the trough, because three cross-braces lifted it above the ground. My first real job using a staple gun. I don’t know why the staples didn’t go right in, but “If in doubt, use a hammer”.

I should have stripped away ALL the old plastic before laying out the sheet; awkward it is to strip it away while the new sheet is in place. Likewise the batten strips I used to retain the old plastic, they should have been levered off and put away. If you are kneeling to do work, make sure you sweep away all tacks, nails etc before you kneel. The ragged strips at the end, too, should have been stripped. Next time I will …

I made liberal use of my bottle of wood glue. Those two old rusted tacks, they too ought to have been removed. I have been putting off this job for a month, and was fired up and too eager to get it done,

My sheet climbs over one of the three cross-braces that hold two plans together. That white batten should have been removed, but the black cross-braces stays. There is therefore a gap where the plastic sheet climbs up to cross the brace.

I will slit the plastic to make a closer fit, glue and staple, but leaving a vulnerable entry-point for the wind. By January 2nd (!!!) this year we had had gusts up to 93 Km/hr. Last January the maximum gust was 140 Km/hr.

This version is supposed to prevent gales ripping away the plastic sheet.

So why am I leaving a little gap? I reason that the gales can’t rip off the sheet if there is no way for the gales to pass right through the sheet. I am depending on a sealed barrier on the other side, or perhaps enough very small gaps to dissipate the force of the gale.

I have now stapled the edge of the plank and the underside. I am getting better at glue. Each row of staples must be hammered down.

Now this is a near-perfect gluing. I squeeze the glue, stretch the plastic, then run my thumb along the edge to smear the glue an inch wide before stapling.

Here is the trough, laid out flat. Some glue dripped down in an earlier phase.

Initially I had thought to glue the sheet right across the trough, but decided that that was overkill. Besides, I already have plans for version six!

The far edge id triple-stapled with glue.

The original tacking was a staple every foot or so. Should I pull out the initial staples and stretch the plastic for this second side? I decided against it. The hinged trough frame is not orthogonal, so no matter what I do, I will never get a true straight line at the bottom of the plastic sheet “V”.

Done! (almost). The trough sheet is stapled and glued along both long edges. Now I have folded it up.

Down the left-hand side of this image you can see the huge faux-leather hinges I installed last summer.

In this view two of the black timber cross braces can be seen. They will not be needed for version 6.

I will leave the glue to dry overnight, and tomorrow morning will deal with the two ends, preferable propping the trough on the table so that I don’t wreck my knees and back by working on the floor.

Ideas for the Sixth Generation

This trough is about nine feet long with two sides of two feet each. The timber came when Lloyd and Selwyn stripped siding from the convenience store in spring 2019. By then I had seen how much rain could be collected in a 15-inch wide plastic drawer.

Four years later I believe that I do not need a two-foot wide throat.

Rain falls off my roof (no eaves troughs), and gets blown this way and that. The wider the throat, the more rain water I catch. But I catch much more than I use, perhaps three times as much.

So my next version will not be a wide-throat trough cobbled together from left-over scarps of timber. It will be a sold device mad from two planks of the widest timber I can get from Swyers. And if it is only eight-feet long, no matter.

Remember that I am capturing water from an eight-foot length of roof that itself is ten-feet to the ridge. That is, my catchment area is eighty square feet.

If I’ve done my sums right, January 2022 we had three days with rain above 10mm. That means that that month I could have collected nineteen gallons without switching pails at two in the morning. Last September four days of 10mm or more, and remember, on a day when we get more than 10mm I may harvest a pail during the day and a second pail while I sleep.

A 25-litre pail (of which I use three) is over 5 gallons, so I often collect one pail by the end of the day and a second pail overnight.

If I catch only 80% of the rain with a narrow throat, I will still have more than enough.

Saturday, January 14, 2023

The nine-foot rain trough is complete, stapled and glued on three sides around all four sides of the wooden trough. Both ends could be crept in a little closer to the wall.

Predicted rainfall is 25 to 50 mm to Tuesday morning. That should yield me over 80 gallons (if I run outside at 2am!)

The view from the shed. Note that the lower end of the trough (where the rain water trickles out) is adjacent to my door. I don’t bother putting on a coat to collect the pail. In this photo my black pail is filling up. I shall let it overflow and then tip out the collected water. There is enough rain to use it to rinse my pail!

The view from my back yard. There is quite an incline on the trough.

Search