Harvesting rainwater

Underground rainwater reservoir.

Harvesting rainwater for your home means not consuming microplastics that proliferate in both the .

  1. Bernard Preston
  2. Our green home
  3. Harvesting rainwater

By Bernard Preston

We do not actually use water; it simply passes through our homes, bodies and gardens on its way from some dam and eventually back to the ocean via a river; some of course evaporates.

More than enough lands on your roof in an average month in a summer rainfall area to supply all your needs for the whole year.

Like the free electrical energy landing on our rooves, the main problem is storage of that water; you have to be able to save enough for the long winter period.

More sensible is not to go off the municipal supply completely, but store enough for perhaps a couple months.

In 2016, for half a year, the KZN midlands, for example, had only 60mm of rain, but that is very exceptional.

Thankfully the summer rainfall pattern has returned and there is more than enough; if you can store it.

The average home might use about 20 kilolitres per month; storage of 40kl is the problem. That is enough for an average sized swimming pool. In the end, some compromise is necessary, and we settled for 25kl; it is enough for the average dry winter, and has proved more than adequate in 2016.

A 25mm storm, on a 200 m2 roof would provide 0.025 x 200 = 5 kl. Five such rains would fill our reservoir. Daily usage would be less than one kilolitre. In practice, it’s difficult collecting the water in the gutters on the far side of the house; you might aim to harvest half the water falling on your roof.

Digging trenches and plumbing a series of standard sewage pipes from the downpipes to the reservoir proved very simple and inexpensive; one could add first-flush devices.

Your desire may be simply to go green; to use what the heavens provide instead of relying on your utility to supply all your needs. It may be that you are increasingly concerned that for various reasons that the authorities will in the future not be able to provide a continuous supply of healthy, potable water.

High on the list of contaminants is asbestos from aging municipal water pipes; it causes a very serious bowel cancer called mesothelioma when drunk. Whether it’s E. Coli and other pathogens, break down products from chlorine, acid ground water, or simply no water at all, many South African towns have serious problems with both the provision and quality of water; and the auditor-general reports that the Department of Water and Sanitation is in crisis; it’s not going to get better. You want to be independent of the water woes of the new South Africa. And, of course, there’s the increasing cost of municipal water.

Storage means use of either tanks of the Jo-Jo type, or fibreglass; fibreglass tanks last forever, but cost a bit more. Both have the disadvantage of being unsightly and above ground and pathogens flourish in the warm water. We settled instead for a large underground reservoir, two metres deep and four metres in diameter, with a corrugated iron roof to keep the light and gogos out. A simple filter and pump will provide your home and garden with plentiful, high-pressure water. The total cost was about R20,000 four years ago. Payback time might be ten years, excluding all the health issues associated with polluted water, and the continuing frustration of water shedding.

Plastered correctly, the reservoir shouldn’t leak, but ours did; that meant fibreglassing the whole, an extra cost of R15,000 but we now have zero leaks, and the reservoir in the summer never drops more than a few centimetres.

We drink the water without reserve despite the hadedas that frequent our roof! And haven’t had the slightest problems; you could install a UV light. More difficult are the leaves that trees deposit on the roof. Keeping the gutters clean is an on-going maintenance issue, but should be done anyway.

Going green is not without difficulties; harvesting and storing rainwater is no different. In the short term there’s a considerable expense; in the longer term, having high quality, soft and clean water, free of chlorine in your home, enjoying a generous fifteen-minute hot shower and knowing you are providing for a better world is without measure. To heck with water saving and energy efficient showers! A solar generator easily drives the electric pump that supplies your home with pristine water.

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56 Groenekloof Rd,

Hilton, KZN

South Africa