Tuesday, April 24, 2007

Water water everywhere… except the catchments

Rain has been bucketing down in Sydney over the last couple of days but it has been a different story in the catchments that receive the water for Sydney’s water supply. According to the Sydney Morning Herald, 80 millimetres has fallen in the city’s north and 40-50 mm in the east, but only 10-20 mm in the west and less than 10 in the catchment areas.

While emergency services in the city have been battling overflowing drains, gutters and leaking roofs, dam levels have fallen by 0.3% in the last week.

This underlines the problem with having Sydney’s water supply piped from areas that are much drier than Sydney is.

Some possible solutions? Catching some of the stormwater and diverting it for industrial uses is one. Rainwater tanks for homes are another. A report last week commissioned by the Australian Conservation Foundation, Nature Conservation Council (NSW) and Environment Victoria examined The economics of rainwater tanks and alternative water supply options (pdf).

The findings are not very surprising: water tanks are most cost effective in areas where there are high rainfalls and for houses with large roofs (where they can collect more water). There are plenty of those areas in Sydney. The cost per kilolitre for large tanks in high rainfall areas is less than a small desalination plant and not much higher than a larger plant. When you factor in the reduced pressure on stormwater systems and emergency services that comes from diverting some rainfall during storms into household water tanks, it’s a fair bet that the social cost of water tanks is lower than desalination. When you factor in environmental costs, rainwater tanks become cheaper again: a desalination plant powered entirely from green power, as has been promised by the NSW Government, is a fairly expensive proposition.

However, there’s another very cheap measure that doesn’t get much attention: you can divert rainwater from your downpipes directly onto your garden – or your pool, if you have one. You can buy a diverter for less than $40 (I found a few websites from distributors) and your rainwater can go straight into a hose and out onto the garden. (‘Raingardens’ are popular in the USA).

Now, I don’t know how much this would reduce your water consumption by – after all, gardens are getting watered anyway when it rains – but it’s essentially zero cost and reduces pressure on stormwater systems. And it means your garden gets a thorough soaking when it rains. I lived in a house in Sydney a couple of years ago where the downpipes diverted directly into two garden beds and they rarely needed watering.

For backyard pools, it makes no sense to fill them from mains water when this option is available: an added advantage is that rainwater is much warmer than mains water.

Industrial water recycling and desalination may well be attractive measures as the drought continues: but household level measures can make an important contribution at a modest cost.

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