MAIL: Rainwater Feedback from Down Under

Screened Floating Intake
Common in U.S. designs, the intake screen in this primary tank floats just below the surface, avoiding both “floaters” at the top and sediment at the bottom.
Screened Floating Intake

I was intrigued by the potable rainwater article in HP149, as I usually am by any articles from the United States on rainwater collection for drinking. Here in New Zealand, I was brought up in a rural area where our only supply of domestic water was from the rain. The main water tank was on a stand at such a height that the rainwater from the painted corrugated metal roof fed into it by gravity and the tank then gravity-fed all the household taps—bath, toilet, etc. Once this tank was full, it overflowed into a large, uncovered concrete backup tank. Occasionally, in very dry summers, we had to hand-pump water from the concrete tank into the tank on the stand.

Our seaside holiday house, along with all the others on the bay, is supplied with water piped from a stream. We have fitted a fine-mesh line filter to this supply, as without it, the filters on the dishwasher and automatic washing machine were inclined to block up with algae. It is much easier to wash out the line filter periodically than to clean the individual appliance filters.

We recently visited Tonga, where our church work-party was improving a water supply system. There, the town water supply is not working much more often than it is “on,” and the most reliable water supply is from rainwater collected from corrugated metal roofs—some of them painted, though many not. Apart from the tanks generally having lids and, in Tonga, having insect screens across the openings, none of the filtering or sterilization measures in the Home Power article have been taken.

While I have read about first-flush diverters, I have never seen or made one. Neither have I come across anybody actually using a floating intake or ozone disinfection units on a domestic supply. I do not recall hearing of anybody suffering any sickness as a consequence of drinking from such water supplies. (There is now Giardia in some streams in New Zealand, and a water supply from one of those would need a filter to help prevent illness from this parasite.)

We do take some precautions that (somewhat surprisingly) the article did not mention. For instance, not all roof paint is appropriate. The label on the paint container I have says: “Safe water collection: Suitable for the collection of drinking rainwater. Important: While painting, disconnect the downpipes from your drinking water collection tank. Do not reconnect until after a significant rainfall has washed any surface surfactant off. Alternatively, thoroughly hose the roof with water before reconnecting.”

Is the rainwater in rural areas of the United States really that much more polluted than it is in the South Pacific? Or is it that people there live in such an artificially sterile environment that they have not built up any immunity to anything and so need to take such precautions? Or is most of it overkill?

Lindsey Roke • Manukau, New Zealand

You pose some great questions. Let me say first that if it works, don’t fix it. If the simpler system people are using in your area to collect and distribute rainwater is working fine, then by all means abide by the KISS (Keep It Super Simple) engineering truth—it’ll be less expensive, with less maintenance and easier-to-find parts.

Regarding the first-flush diverter, there may be more pollutants stateside than in New Zealand. We certainly have a fair amount of tree cover in many areas, which can lead to contamination from bird and squirrel droppings that wind up on the roof, and widespread use of coal for electricity generation, which means a dusting of mercury-laden soot can build up on our roofs within hundreds of miles of the power plants. Additionally, leaves and other organic matter have the potential to act as a reservoir for unwanted microbes should some get in the cistern. So flushing this buildup, especially after a prolonged dry spell, is a great idea.

A tank just 10 or so feet above the home will provide usable water pressure, as you mention, but it will be much less pressure than what we are used to here (between 30 and 60 psi). A 40-foot (or taller) tower will provide more than 17 psi. Of course, conveying the water to this tower requires a pump, and said pump might as well be supplying your household water pressure as opposed to the additional expense (quite substantial) of a tower.

Rainwater collection in the states is a more novel endeavor than in New Zealand and Australia. As such, it may be a combination of our stomachs not being used to drinking local, unfiltered water, as well as not wanting to give rainwater collection a bad reputation by having someone get sick; that leads us to use sterilization procedures. I would certainly go to the trouble of having your tap water tested and analyzed to make sure there are no hidden troubles lurking there like heavy metals leaching from lead solder in the metal roof and gutters or a pathogen that might sicken a person with a less robust immune system than yours. The state of Victoria in Australia has a great checklist for rainwater collection ( 

Here in the United States, we are just recently rediscovering the many benefits of metal roofs. As such, many new metal roofs come with a factory finish that is safe for rainwater collection. The need to address repainting rarely occurs, at least for now.

Stephen Hren •


Comments (1)

althea's picture

There are actually plenty of natural and synthetic water filtration systems that you can use to filter water and make it consumable. Here in AU i'm using the natural filtration system.

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