Make flood safe drinking water easily

Make flood safe drinking water easily…

Safe water is the most important problem in floods . But we can make the flood water suitable for drinking, if we can kill the pathogens of diarrhea, typhoid, cholera etc. in it. And this work is not difficult. A few such methods are highlighted here.

Boil in the oven

Boiling water is an ancient method. But in earlier days it was said to boil water for 20 minutes. Modern research has shown that there is no need for it. Water boils at 100 degrees Celsius. A few moments at that temperature are enough to kill germs. Then I can stop the heat when the water starts to boil. So you can boil the flood water in the stove and drink it, you don’t have to go far for safe drinking water. But first strain the muddy water with a thick cloth or several layers of cloth (sari, lungi or chadar). Better if you can use alum to settle the floating dirt down.

However, it can be difficult to get stoves and fuel to heat water during floods. So, below are some methods of how to easily sterilize water in sunlight. These systems can be installed in any high place and even on rafts.

Solar pasteurization method

Harmful bacteria are killed by heating the water to just 60 degrees Celsius and keeping it at that temperature for half an hour. And at higher temperatures it works in less time. For example, it takes only 15 seconds at a temperature of 70 degrees Celsius. This process is called ‘pasteurization’ after the scientist Louis Pasteur. Water can be easily pasteurized and disinfected by sunlight. For this, several devices are available abroad. But we have an invention, which is cheaply available in the local market, that has been able to effect the famous ‘green house effect’. As a result, the water temperature can be increased much more than 70 degrees Celsius. Anyone can make it themselves. Don’t have to sit down to get supplies from anyone.

For this method I will use the system of black painted bamboo branches. Its diameter was about 30 inches. But a bed of straw about four inches thick must be required under the branches. For this bed, it will be convenient to put the straws in a big polythene bag and close the mouth by heating or stitching. Because this work has to be done every day. Moreover, if it rains, the straw will not get wet. It also requires two large (about 4 ft x 4 ft) transparent plastic sheets. With it, the bamboo can be completely covered and kept taut with weights on all four sides. But there should be an air gap between the two sheets, not sticking anywhere. For this, in the system we used several rings made of thick paper with a height of about half an inch. To prevent the bottom sheet from sticking to the bag filled with water again, there will be a few similar rings. That is, there will be an air void layer over the water-filled bag, Again, there will be an air gap between the two transparent sheets. The height of the edges of the bamboo branches will come in handy for this. If you look closely you can see two layers of paper rings. A ring can be made by cutting a paper strip and glue it or stapler pin.

SODIS or Solar Disinfection System

The method, developed at the American University of Beirut in the 1980s, has been promoted by the EAWAG Center in Switzerland. Fill a clear and clean pet bottle (bottles where drinking water is supplied in the market) with water and keep it in clean sunlight for 6 hours. It does not heat the water as much, but the ultraviolet rays of the sun kill harmful bacteria in the water. Use bottles of two liters or less. Because the water in the larger bottle is deeper, the ultraviolet rays cannot reach the bottom. For the same reason the water needs to be clear. If the water is cloudy, the ultraviolet rays cannot penetrate to the bottom of the water. In this case, use alum as described earlier or strain it with a thick cloth.

If pet bottles are not available, you can sterilize water in the same way using transparent polyethylene (PE) or polypropylene (PP) bags as shown in Figure 2. Here we have used bamboo sticks painted black with enamel paint. Spreading these bags over it will give better results. Because black color will absorb sunlight and heat up. This heat will be transferred back to the water, as a result the temperature of the water will rise a little. Increased temperature and ultraviolet rays—combined to kill germs more quickly. It is better if a thick bed of straw or dry leaves etc. can be placed under the bamboo branches. Then the heat will not be lost downwards and the water temperature will be slightly higher. If the depth of water in the bag is less, it will work faster. If you fill the whole bag with water, it will be too deep in the middle.

Fill a transparent high density polyethylene (HDPE) bag one-third full with water and twist the top to expel the remaining air. Then close the open mouth with glue on top. As a result, there will be no air inside, but the water will spread if the bag is dropped on the ground. So its depth will also be small (less than an inch, like a fingertip). In this condition, spread the bags filled with water on any flat surface in the sun for 5-6 hours. Bamboo dalai is not what it should be like in the picture. You can also keep it on flat ground or on bamboo mats, bowls, big plates etc. However, if the rice is placed in a sloping tin, the water will accumulate under the bag and the depth will increase, then the ultraviolet rays will not reach the bottom. So don’t put it on anything sloppy.

In the picture we have used black dyed bamboo shoots. Spreading the bags over it will give better results. Because black color will absorb sunlight and heat up. This heat will be transferred back to the water, as a result the temperature of the water will rise a little. Increased temperature and ultraviolet rays together can destroy the germs more quickly. It is better if a thick bed of straw or dry leaves etc. can be placed under the bamboo branches. Then the heat will not be lost downwards, so the temperature of the water will be slightly higher. If the depth of water in the bag is less, it will work faster. Spread several such bags together on a black bamboo stick. Since the depth of water is shallow, and the temperature is slightly higher than the PET bottle system, the water will be sterilized in about 4 hours.

Microbial testing and practical applications

Microbiological scientists from Dhaka University’s Department of Microbiology and Center of Advanced Research in Sciences have conducted many experiments on this pasteurized water that we have invented. They have seen that if kept in the sun for one and a half hours, all the germs of water-borne diseases such as diarrhea are destroyed. It remained sterile even after six months when properly stored. Around 300 Bede families in Barisal have implemented this system through the efforts of two NGOs, CMES and ‘Social Development Organization’. For about three years since 2002, the people there have met their drinking water needs by building the system of bamboo branches themselves. Besides, a teacher of Ulab was able to successfully introduce the folding table system in Rai Bazar Basti of Dhaka with personal efforts. All of them are directly involved in this work.

Special precautions

We know that throwing polythene bags anywhere causes huge damage to the environment. So first try to recycle polythene bags as much as possible. When destroyed, store the torn polythene bags in a large bag instead of throwing them around. When enough accumulated, sell it to plastic waste collectors.


Many students-teachers-researchers have worked on our project since 1982. Everyone’s effort is behind it, so credit goes to all of them.

Cooperation in the present context

In the current flood situation of the country, if anyone wants to use our system to provide safe water to the flood victims, please contact us at Dhaka University. Initiatives can be taken to spread this method in other countries of the world.

Rainwater harvesting

Rainwater is basically distilled water, which is pure. It has no germs. Rain that falls only in the first few minutes may contain airborne dust particles, etc. So it should be collected five minutes after the start of rain. However, water collected from tin roofs cannot be directly drunk, as it may contain bird droppings, rotten leaves, etc. In our invention we used a polythene sheet, which is dried and kept clean at home. Make four loops or rings by tying thin plastic ribbons or ropes to the four corners of the sheet beforehand. Always bury four thin bamboo poles in the ground in an open area (not under a tree). The distance between the two poles behind it will be greater than the distance between the two poles in front. Whenever it rains, Then the square loops of the sheet are stuck on the head of the pole and the polythene sheet takes the shape of a funnel. A clean bucket placed under the funnel will collect enough water. Store this water later in a clean pitcher. This water can be drunk directly. If one is storing rain water in other ways and it is likely to become sterilised. But it can be sterilized by solar pasteurization method. On cloudy but not rainy days, since solar systems won’t work, always keep some extra water handy.

Apply at normal times as well

The above techniques can be used without flooding. In particular, where arsenic is a problem, these technologies can provide a simple solution. According to British Geological Survey report, there is arsenic in water from 70 feet to 300 feet deep in Bangladesh. Water from rivers, streams, canals, ponds comes from rain water, snowmelt water, etc. So there is no arsenic in these waters. As this water seeps through the soil and accumulates in the aquifer below, it is contaminated with arsenic in the underground rock along the way. If there are no rivers, ponds, etc. in the vicinity of the arsenic area, 40/45 feet deep tube wells or shallow wells can be installed to disinfect the water using the above technology. Again, in mountainous areas, many people store roof water in large quantities. But it is easily contaminated, not drinkable. That water can also be sterilized using the above technology.

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