It’s a hard rain a-gonna fall…

"Oh, where have you been, my blue-eyed son?
And where have you been my darling young one?"

"I've stumbled on the side of twelve misty mountains
I've walked and I've crawled on six crooked highways
I've stepped in the middle of seven sad forests
I've been out in front of a dozen dead oceans"

"I've been ten thousand miles in the mouth of a graveyard
And it's a hard, it's a hard, it's a hard, it's a hard
It's a hard rain a-gonna fall"

The much-awaited rain came late yesterday afternoon with such excitement you’d swear we live in a desert or something.

Well, sort of excitement. Because we wanted to see how effective the cleaning of the downpipe had been, and how efficient the water harvesting process has become. This can only be determined if you have a reasonably substantial downpour.

The weather forecaster had promised that the lower half of North Island would get such a substantial shower or two late Sunday, and true to form, he was correct.

We work on the following criteria:

Main tank dimensions: D =3.00, h = 2.400
From my old maths formula:  Pi r²h = 22/7 x 1.700 x 1.700 x 2.400 = 21.79Kl

Allowing for the overflow to the secondary tank and ullage allowance, the tank therefore has a nominal capacity of 20,000 litres. A 2.4 metre length of profile beading salvaged from the shed and marked off in 220 mm graduations by Tyler produces a practical and durable dipstick… as long as it stays in one piece.

A dip of the tank at 11:00 am shows that the level lies at the 12.25Kl mark. Now bring on the rain!

The roof area is approximately 250 square metres. Therefore, assuming optimum efficiency and minimal leakage and loss, for every 1mm of rainfall, we should collect 250 litres of potable water.

This morning, we dipped the tank once more, and within the limits of practical accuracy, I am please to report that the approximately 19mm of downpour last evening caused the level in the tank to rise to 17Kl, being about 4,750 litres. Quite conveniently, 19 x 250 litres is precisely what we were expecting.

Like all good scientists, we will repeat the exercise when the next heavy rains come. In the meantime, Tyler is busy preparing the overflow tank so that we don’t waste any precious water.

Can you feel the excitement? Next time you open a council-supplied water-tap, please remember those who look towards the skies for theirs.