The pure truth about our water

Another Life: The water I pour from the rain-gauge bottle into a calibrated glass beaker these bracing autumn mornings has a chill clarity surpassing even that of Bombay gin. Sometimes, after counting off the millimetres against the sky, I drink them as a toast to the ocean from whence the raindrops came.

The water tastes enjoyably of nothing, which is better than most urban folk can say these days, but can it be as pure as it looks? I once assisted science by dashing out to bottle individual Atlantic showers for several stormy weeks of winter: a team of soil researchers wanted to analyse their chemistry. They found, as I recall, more sulphur than expected, which was generally good for grass. This is how the ocean feeds back to the land the sulphur washed out in rivers, a typical piece of Gaian thriftiness.

Does water need such natural additives to be good for us? Mountain minerals are the boast of famous bottled spring waters such as Evian, Perrier and Apollinaris. Ballygowan draws on a deep limestone aquifer in Co Limerick, which builds the bones of great cattle and hurlers. Indeed, there's been keen debate as to whether distilled water - purest, most neutral (and tasteless) of all - might actually do harm if drunk long-term.

Some think it's naturally "hungry" for the mineral particles it lacks, leaching them from your body (your hair will fall out, your blood pressure rise); a few testy doctors on the web, on the other hand, say nonsense, they drink nothing else, and besides, the body gets its minerals from food, not water.

A bubbling hill stream, fed by ocean rain, filtered by mountain peat and bouncing down over the rocks, can seem the epitome of natural purity. Those of us who live below the streams of sheep country and fill our taps by gravity through plastic pipes, have learned to appreciate the water better when its particles are intercepted by fine steel mesh and its E.coli zapped with ultra-violet light.

As for holy wells, springs and subsurface water in general, these were the subject of a fascinating contribution to a recent major conference of geologists in Dublin. In a paper called Mystical Mythical Ireland: Groundwater and the Advantages of Suspended Disbelief, hydrogeologist Dr David Ball engaged head-on with the "pre- Enlightenment thinking" that stops so many Irish people from considering where their water comes from and how to keep it safe to drink.

Why is it, he asked, that our society has such a sense of mystery about the subsurface and the fluid flowing through it? Why, out in the field, does any conversation about groundwater have to bring in holy wells and water diviners, and why do most people believe that water flows uphill, as if by magic, to emerge as springs? Ball blames pagan myths absorbed into Catholic culture. To cast any doubt on the sacredness and purity of holy wells, he suggests, challenges both the church and an ancient sense of place: the State even prints "Holy Well" in red on the latest maps.

As Ball described in graphic terms, many of the wells lie at the bottom of slopes in active graveyards ("essentially a low- intensity landfill site for organic waste") or downhill from fields regularly spread with cattle slurry. But "it is comforting to the psyche to leave the subsurface as a mystery" and this remains both explanation and excuse for all manner of ignorant pollution.

I have to confess to thinking (or not- thinking) that springs did, indeed, leap out of the ground much of their own accord, rather than under the laws of gravity. (And the wife's father was a dab hand with a forked twig, no matter what they teach in UCD.) All that said, it is amazing just how long some of the key ideas about the earth have been around, and what gifted imaginations have conceived them. Anaxagoras, born about 500 BC, worked out that the sun draws up moisture from the sea, which then falls elsewhere as rain to supply rivers and cavern waters. Aristotle (born 384 BC) went on to develop Anaxagoras's concept of this natural cycle, keeping evaporation and rainfall in balance.

If you feel wonder about the earth's behaviour and the marvellous lurches of historic human insight and analysis, you might enjoy a booklet just published by Dr Paul Mohr, the retired professor of geology at UCG.

Discoverers of Earth's History abstracts the highlights of the growth of geological understanding from the ancient Greeks to Darwin, traced through a list of 150 scientific thinkers. It was compiled "to beckon and foster the interest of seekers and students" and speaks volumes for Mohr's delight in communication. It is available from Millbrook Nova Press, Toin an Gharrain, Cor an Dola, Co na Gaillimhe, priced €13 (inc p&p).