Rainwater in Cities

Dear Margaret,
We have our own vegetable garden as well as an area of native plants. We live close to a main road as well as a major freeway. We would like to have our own water supply to water our plants, although we have been warned that the pollution from the passing traffic would endanger the plants. Could you give us information on a safe way of collecting rainwater?


I am not sure whether, when you use the term 'endanger' you are referrring to plant damage or plant contamination. Damage to plants is caused principally by acid rain, which is as yet much less common in Australia than in Europe & North & Central America. Also excessive dust on the leaves does retard plant growth. You have, however, to deal with contaminants such as traffic fumes, & the dust, which may be strongly alkaline or saline, & contain heavy metals, including lead.

Unless there are industries up-wind of you which burn coal & do not clean the emissions, rainwater from your roof should be quite acceptable for watering, if before you install the tank or cistern, you choose one of the various clever devices, available from most hardware stores, which allow the first gush of water to wash your roof & gutters clean & flow into the storm water drain, then divert the water into your tank for as long as the rain lasts. Clean roof & gutters, clean water - simple!

To check the Ph of the water, I don't see why you shouldn't use an ordinary soil testing kit. Just mix a few drops of the water collected from your roof with the white powder & check the shade against the card. Then test your soil. Neutral is 7, & most plants are happiest at about 6.5, or slightly acid. (The instructions included with the kit should give you plenty of information about Ph levels.) So if, for example, your rainwater is 5.5 or 6, & your soil is 7 or 8, you shouldn't have any problems. Plants have the capacity to change the Ph of the soil around them anyway, if you give them plenty of humus & don't over water them. So I really wouldn't worry unless I were getting extreme readings. If you want a complete analysis of both soil & water, & are prepared to pay for them, your local Dept. of Primary Industry, or it's equivalent, should be able to reccomend someone. Or look in the Yellow Pages under horticultural or Agricultural services.

If you want to know what areas in your city could be affected by acid rain or heavy industrial pollution, contact your local Dept. of Environment, or EPA, & your local Health Dept. If they are unhelpful & you want to do the investigation yourself, you will need detailed maps & weather information, especially about prevailing winds, & lots of information about local industries & traffic flows. The Dale Street Women's Centre in South Australia got a grant to do just such a survey, because they were concerned about the effect of local industries on air quality & their children's health.

Here are some useful tips for inner city gardeners:

Please continue your gardening in the city. If you feel the need for support, contact your local Permaculture or gardening group. Only a privileged few can support themselves in rural areas. If you are not convinced, try dividing the world population into the total cultivable land areas of the Earth - your local library will have books containing the figures.

We can, & MUST, re-earth the cities, making them pleasant & sustainable places to live.


Note: In researching & answering questions about earthwise living, Margaret offers information, opinion, & personal experience, but no quick fixes! Readers should evaluate these offerings in the context of their own situations; they are suggestions, *not* recommendations. Any responsibility for their implementation rests *solely* with the reader.


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