The world's clearest water
VulcanSpirit
Richard & Alison Brunstrom
Tue 17 Dec 2013 09:17
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As you may be aware New Zealanders are keen to
claim "the world's best/biggest/tallest etc", despite having little that really
justifies it. But they do have some very cleanwater. This is Te Waikoropupu
springs near Takaka in the north of South Island. The water here has a
visibility of 63m which is very clear indeed - the theoretical visibility of
pure distilled water is only a bit better at 83m.
 The water emerging here is just over 10 years old,
having fallen as rain in a large limestone catchment. It seeps down through the
rock underground until it reaches a large granite mass which forces it to the
surface at an average rate of 14 000 litres per second. Put in context,
that's about the entire consumption of the city of Boston MA (but only the 90th
biggest spring in the world). Interestingly by this stage the water is very
slightly salty. The explanation seems to be that the fresh water has sunk below
sea level. When it is forced to the surface by the granite a venturi effect
sucks up a small amount of seawater which has penetrated inland - the only place
in the world (here we go again) where this is known to happen.
But even this isn't the clearest fresh water in the
world; that honour belongs to Blue Lake in the nearby Nelson Lakes National
Park here which has recently been measured as 70-80m - really quite
astounding. A true 'best' for NZ.
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