TRIZ Challenge - September 2002

TRIZ Challenge - September 2002

We challenge you to use your TRIZ skills and your knowledge to help solve a humanitarian or social problem. We hope that you will submit your results for publication in the TRIZ journal. Every few months we will set a new challenge - but that does not mean that you cannot continue to work on previous challenges, indeed you may have chosen to work on this for your project or coursework.

Send your results, ideas, comments and suggestions for future challenges to

This month's challenge is an engineering challenge with a humanitarian aspect. How can you purify water for drinking in a subsistence environment in a developing country such as Zimbabwe?

More than a billion people lack access to clean drinking water, and millions die every year from water related diseases.

Filters can remove insects, larvae, worm eggs and cysts but allow bacteria and viruses through. Membranes rely on you being able to keep the clean side sterilised and are delicate. Chlorinating requires chemical additives and does not kill all bacteria (look what lives in your swimming pool). Heating uses fuel and far from killing them, can cause some viruses to accelerate their growth.

Can you devise a cheap and portable method to 'clean-up' water to make it fit for drinking. The method needs to be simple to operate and cheap so that no-one is excluded from using the method.

Can you think of a method that could be used in conjunction with last month's challenge (a water pump for the developing world) such that a proportion of the pumped water is suitable for drinking.


Trevor Baylis (the inventor of the combined wind-up and solar radio) has applied his mind to this. His company produces a device that you pull up a rope, which is secured to a tree, this winds up the mechanism and as the mechanism falls a voltage is produced that is conducted from the rope through the water to the bucket. If there is no natural salt in the water this is added (a few grains), the chlorine from the salt and the hydrogen from the electrolysis sterilise the water. The disadvantages are: initial cost; may need to purchase salt; some organisms can survive the process (admittedly not many); and you need a tree or tall structure (you don't want to wind it, otherwise the current flows to ground through you). The advantage is that it is quick (2 minutes) and 99% effective.

The WHO (World Health Organisation) and UNICEF are promoting a scheme that uses discarded clear PET bottles (such as you might buy a couple of litres of lemonade in). The bottle is filled with water and placed on a black surface in the sun for most of the day (they suggest around 5 hours). The temperature rises in the bottle (the water and bottle form a lens to heat the black surface and the water), the ultraviolet radiation from the sun kills the viruses in the water. Advantage is that cost is effectively zero. Disadvantage is that not all pathogens are killed (typically less than 1% survive), particularly if harbouring in the cap or the moulding of the base. The bottle cannot get too hot otherwise the plastic deforms and the bottle splits.

At present this is probably the best, cost effective solution. Can you improve on it?

In Mediterranean countries, a beach barbecue can be cooked using flexible silver film (like Aluminium foil) that forms a parabolic cooker and folds up smaller than a bikini when finished. This can get food very hot very quickly. Could this simple technology be utilised to pasteurise the water without destroying the container?

Wateraid describe on their website describe the problems that we face in providing safe water for the entire world (something most of us take for granted).

Oxfam's latest campaign (see their web site: is the establishment of water supplies in Goma. The aim is to provide 15 litres of clean water per day per person.

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