Tuesday, February 06, 2007

Tuesday Column: Why recycled water is hard to swallow

I have actually sipped from a bottle of recycled sewage. And I have to tell you that it tasted odd.

Not because the water tasted like sewage, quite the opposite. It was unnaturally lifeless, sterile. It made me want to gag.

Professor Greg Leslie from the University of NSW who gave me the bottle confided that that’s quite a common reaction when tasting completely cleaned sewage. The sensation is outside of our usual experience.

The reasons why tell us a lot about the safety and nature of what we are likely to be drinking in Canberra in 2010.

But first I better tell you how I came to be drinking recycled sewage...

Greg Leslie found me a couple of bottles of so-called NEWater, direct from the output of Singapore’s sewage treatment plants. Our plan was to chill the bottles to make the water palatable and then present them to members of the audience of the SBS TV program I was working on. The program’s host Jennie Brockie was worded up and after a vigorous discussion between experts including Malcolm Turnbull and the heads of state water authorities she called for volunteers to drink the stuff.

‘Justin’ volunteered but just held the bottle. “Don't just look at it, drink it!” the presenter yelled. Justin put the bottle to his lips, swallowed and said it tasted fine. ‘Camilla’ tried some and exclaimed with surprise: “It's water! Before I walked in here I thought no way, but there's no smell, there's no smell!”
It is true that recycled sewage does not smell, but it is not true that it tastes like water. As Greg Leslie explained to me, it has no taste whatsoever, something we find hard to handle. As soon as any sort of substance enters our mouth we instinctively search for some sort of taste in order to work out whether it is safe to swallow. If we can’t find one our reflex is to gag.

Recycled sewage has no taste because of the way in which it is created. After normal treatment it is forced through a membrane with holes so small that nothing bigger than a water molecule can get to the other side. As the Singapore NEWater propaganda tells it, if a water molecule is the size of a ping pong ball, a hormone is the size of a soccer ball, a virus is the size of a truck and a bacteria is the size of a skyscraper.

But it is not that simple. So small are the holes that on one interpretation they are not holes at all. They appear to block things other than water molecules regardless of size. In the strange world mapped by quantum physicists it is arguable that the water molecules disappear on one side of the membrane and reappear on the other without passing through.

The resulting water is unnaturally pure. And unstable. The molecules attempt to latch on to anything they can find, corroding concrete pipes.

It is also very valuable.

Singapore produces 92,000 cubic metres of NEWater a day, but only a fraction goes into the water supply, providing just 1 per cent of the island’s daily water consumption (due to climb to 2.5 per cent by 2011). Most of it is diverted for use in the manufacture of Singapore’s precision designed silicon chips. Only totally pure water can wash away the impurities from the chips without shorting the circuits. As the Singaporeans see it NEWater is too valuable and too refined to be wasted on humans.

It is certainly safer than the water enjoyed by the residents of Washington DC. Recycled sewage is piped into their dam without being membrane treated. It is safer than the water enjoyed by the residents of Adelaide who get our sewerage piped into their dams without membrane treatment. And it is probably at least as safe as Canberra water (and would taste as good when salts are added and it is mixed with our dam water).

But it isn’t completely safe. Greg Leslie’s frustration is that nothing is. He says the risk of contracting an infection from drinking two litres of recycled sewage each day for a lifetime is about 1 in 10,000, which he says sounds high but is 100,000 times lower than the risk of infection from drinking the same amount of tap water per day.

The National Water Health Risks Working Group is finalising its draft guidelines for the expected quality of the treated sewage used in drinking water, and they are expected to be standards that modern filtration plants can comfortably meet. Technologically, there is nothing much holding recycling plants back.

Financially, recycling plants are a better option than most of the others for supplying extra water. A report prepared for the then parliamentary secretary for water Malcolm Turnbull in November found that recycling sewage was likely to be cheaper than building extra dams, and much cheaper than installing rainwater tanks. In this respect the Prime Minister has set a bad example. He has promised to install a rainwater tank at his residence at Kirribilli.

Recycled sewage also has the advantage of being constant. We are always creating it. It doesn’t dry up during droughts in the same way as dams and rainwater tanks can.

The biggest concern from an engineering viewpoint is that a plant might break down unnoticed, pouring dangerous inadequately treated sewage into our dams. To me this seems a small risk, worth taking. We put our trust in technology in so many other areas of life and usually it is rewarded.

The real problem that most of us will face in the transition to drinking recycled sewage is emotion. There are very good reasons for our instinctive revulsion to human waste. In most parts of the world they haven’t been overcome. Where sewage does enter the water supply it usually does so “accidentally” as is the case in London, France and along the River Murray or indirectly as it does for the membrane treated water pumped into the aquifers under Orange Country in California.

Canberra, or whichever city in Australia does first take the plunge of pouring recycled sewage into its dams will be a world leader.

And there are reasons to believe that Canberra residents are likely to accept the idea more readily than the citizens of any other Australian city. All the polls show that the more educated, the more white collar the job and the higher income is the citizen the less revolted that person is about the idea of having treated sewage in his or her drinking water.

I feel good about it, but then I have tasted the stuff and know that it is as far from tasting like sewage as it is possible to be.

When Singapore was softening up its population for NEWater it gave away 1.5 million bottles of the stuff.

Perhaps the head of ACTEW Michael Costello should import a few hundred thousand bottles from Singapore and do the same.

But I would advise him to add salt first.