Volcanoes play havoc with your water. Let's get to the point very quickly

Volcanic ash contamination of water supplies

                        Bore water                 Roof - fed

Chemical -            Low                            High

PH-                         Low                            High

Turbidity                Low                            High


Chemical

The types of minerals present in volcanic ash are dependent on the chemistry of the magma from which it was erupted however elements mostly found in magma are silica and oxygen.

The various types of ash produced during volcanic eruptions from light to dark coloured ash most containing 45 - 55% silica which is rich in iron and magnesium, not the things you want in your water supply!

Gases released during volcanic activity are water, carbon dioxide, sulfur dioxide, hydrogen, hydrogen sulfide, carbon monoxide and hydrogen chloride. These elements mixed with moisture form things like Hydrochloric and Sulphuric acid known as “Acid Rain”

Fluoride

Excess fluorine is recognised as the most hazardous leachate in water supplies, but few historical eruptions are known to have resulted in fluorine poisoning in humans. The main concern of fluorine poisoning is for livestock, which graze on ash-contaminated grass and feed.

Whakapapa eruption has excessive fluoride levels in the ash, up to 6ppm in some areas; these levels are considered dangerous to sheep and other live stock.

Potentially harmful substances in some volcanic ash are the water-soluble materials called leachates, which are acids and salts. These may be composed of sulphuric and hydrochloric acid droplets with absorbed halide salts making these components of the ash mildly corrosive and potentially electrically conductive.

PH

New Zealands normal rain has a PH level of just below 7 which is quite neutral

Again whakapapa eruption had levels down to 4.4, this is every corrosive. Acidic water leads to corrosion of brass fixtures, copper plumbing, steel tanks, heating elements in hot-water heaters, and concrete.

Turbidity

Water cloudiness that has suspended solids will taste sour/bitter and sometimes metallic. Best advice is to boil water before drinking.

Turbidity can have a significant effect on the microbiological quality of drinking water. Its presence can interfere with the detection of bacteria and viruses in drinking water. More importantly, turbid water has been shown to stimulate bacterial growth since nutrients are adsorbed enabling the attached bacteria to grow more rapidly than those in free suspension (World Health Organization, 1996).

Volcanic ash suspended in water can clog and damage filters at intake structures and treatment plants, and ash can increase wear on pumps and other equipment used in water-delivery systems. Because volcanic ash consists of tiny pieces rock and volcanic glass, ash can infiltrate nearly every opening and abrade or scratch most surfaces, especially between moving parts of equipment. Ash particles easily clog air-filtration systems, which can lead to overheating and engine failure.

During the 1995-1996 eruption of Ruapehu volcano ash fell over a wide area of the North Island. Contamination of water supplies was a common concern, and the public was advised to disconnect roof-fed water tanks as a precaution.

The Best Option

Cover the water tank and disconnect the down pipes feeding the tank, this will give the home owner clean water for a few months, if they use the water sparingly.

In some cases this can be very difficult to accomplish, especially newer enclosed systems.