Updated 05 October 2015

Can we drink our tap water?

Rat-tailed maggots will soon be reappearing in Cape Town. Should we be worried?


How uncomfortable should you be feeling about drawing yourself a nice cold glass of water from the tap?

What is a rat-tailed maggot anyway?

If this beast had been referred to as a ‘drone fly larva’ by the media, I doubt there would have been quite such an uproar. But the words ‘rat’, ‘tail’ and ‘maggot’, with their individual associations of filth and pestilence, and, in combination, their suggestion of some sort of cross-species mutant, turned out to be sensationalist gold.

In fact a rat-tailed maggot is just a drone fly larva: i.e. it’s the immature stage of a type of fly, in the same way that a caterpillar is the immature stage of a butterfly.

The adult drone fly (Eristalis tenax) occurs throughout South Africa, and in other parts of the world as well. It is a bee mimic, which means it looks a lot more like a bee than a fly. It also behaves a bit like a bee, and feeds, poetically, on flowers. The drone fly lays its eggs in muddy, stagnant water rich in decaying matter (i.e. the kind of water you’d be crazy to consider drinking), where its rather peculiar-looking offspring hatch.

The infamous ‘rat tail’ is not a tail at all, but a kind of snorkel that allows the larva to breathe.

Before they turn into a pupa, the larvae leave their watery spot and try to find somewhere drier; this is often when they’re noticed by humans.

How do they get into the water supply?

It is extremely unlikely that rat-tailed maggots will be in treated tap water conforming to South African Bureau of Standards specifications, which are also World Health Organisation standards - and our municipal tap water does conform. What could happen is that, on the users’ end of the system, the flies may find opportunities to lay their eggs. They may get into an open cistern or water tank, for example, or they may be able to lay eggs in the u-bend of a basin.

If you live somewhere that is not served by a municipal water supply e.g. in an outlying rural area, where you might get water piped from a farm dam or a rain barrel, say, then you may have variable water quality and organisms like the maggots are more likely.

What can they do to you?

Rat-tailed maggots themselves really are pretty harmless to humans and other animals; their crime is that they are unaesthetically pleasing. The adult fly has also never been implicated in spreading any disease.

There is one disturbing health issue attached to the appearance of the maggots, however. Harmless they may be, but nonetheless they – or any insect larvae – have no place anywhere in the drinking water supply. The fact that they have been cropping up may suggest that standards in drinking water testing and delivery are being allowed to slip somewhat.

The argument is that if the rat-tailed maggots can get in, then potentially so can other less benign organisms.

How can you get rid of them?

You can avoid an encounter with insect larvae of several kinds fairly easily, by simply not allowing stagnant water to collect in your living environment. Also, keep your bathroom and kitchen clean, and have any rusting pipes and leaks dealt with promptly.

Find out what kind of water holding system your building has, and make sure it’s properly maintained. As a general rule it's better to only drink water from the cold tap; sometimes nasty things can get into hot water tanks and cisterns if they're poorly maintained. In my block of flats, for example, a pigeon drowned in the hot water storage tank in the attic because the lid wasn't on properly. The end result was like a scene from Poltergeist: maggots - the ordinary kind, boiled and quite harmless – emerged from the bath tap when the person enjoying a cleansing soak decided to top up the hot water.

Finally, if your tap water looks or tastes at all peculiar, then stop drinking it and report the problem your local municipal health department. If larvae do appear e.g. in a basin, pour a kettle-full of boiling water or a cup of bleach down the drain as an interim sterilization measure.

If residents repeatedly suffer ailments, like upset stomachs, for which there doesn’t seem to be an obvious cause, then consult your doctor.

What about home water treatment?

Home water treatment systems aren’t generally considered necessary if the water in your area meets specifications, unless you have a medical condition that makes you sensitive to certain substances, and your doctor has specifically advised using a device to reduce these substances in your drinking water.

Installing such a device will no doubt make the water taste better and encourage you to drink more of it, which is a plus – just make sure you maintain the system properly (replacing filters regularly etc), otherwise it may end up worsening water quality. Keep in mind that sometimes less reputable water filter dealers can ‘talk up’ the potential health problems of drinking water.

You could also try bottled water if you find that more reassuring - though the health benefits have not been shown to warrant the extra expense there either.

Other people unsatisfied with assurances by city health officials have opted for boiling their drinking water - which certainly would destroy any potentially lurking organisms. Store such drinking water in the fridge, and change it every few days.

Additional information source:
Picker et al. Field Guide to Insects of South Africa. 2004. Struik. Cape Town


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