Tips and Tricks

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 flood water suitable for drinking if we can kill the pathogens of diarrhoea, typhoid, cholera, etc. in it. And this work is not difficult. We highlight a few such methods here.

Boil in the oven

Boiling water is an ancient method. In earlier days, people 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 on 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. You can install these systems in any high place and even on rafts.

Solar pasteurization method

Make flood safe drinking water with the Solar pasteurization method. Heating water to just 60 degrees Celsius and keeping it at that temperature for half an hour kills harmful bacteria. And at higher temperatures, it works in less time. For example, it takes only 15 seconds at a temperature of 70 degrees Celsius. Pasteurization, a process named after the scientist Louis Pasteur, can easily disinfect water using 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 ‘greenhouse effect’. Sunlight can increase the water temperature 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. Someone must place a bed of straw about four inches thick 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. We can completely cover the bamboo with it and keep it 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. You can make a ring by cutting a paper strip and gluing it or stapling it.

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. To purify water, fill a clear and clean pet bottle 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 litres 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 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 colour will absorb sunlight and heat up. The heat will transfer back to the water, causing the temperature of the water to rise a little. Increased temperature and ultraviolet rays—combined to kill germs more quickly. Place a thick bed of straw or dry leaves under the bamboo branches for better results. Placing a thick bed of straw or dry leaves under the bamboo branches will prevent heat loss and slightly increase the water temperature.

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 polyethene (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. 

If the rice is placed in a sloping tin, the water will accumulate under the bag, increasing the depth. This will prevent ultraviolet rays from reaching the bottom. So don’t put it on anything sloppy. In the picture, we have used black-dyed bamboo shoots to make flood safe drinking water. Spreading the bags over it will give better results. Because black colour will absorb sunlight and heat up.The heat will transfer back to the water, causing the temperature to 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. The shallow water depth and slightly higher temperature than the PET bottle system will sterilize the water 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. One and a half hours of exposure to the sun destroys all the germs of water-borne diseases such as diarrhoea. 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 ‘The Social Development Organization’. For about three years since 2002, the people there have met their drinking water needs by building a 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. They directly involve themselves 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. Sell the accumulated plastic to waste collectors.


Many student-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. We can take the initiative to spread this method in other countries of the world.

Rainwater harvesting

Rainwater is basically distilled water, which is pure water. It has no germs. Rain that falls only in the first few minutes may contain airborne dust particles, etc. We collect the water five minutes after the rain starts. Water collected from tin roofs may contain contaminants, so we use a polythene sheet to filter them out. We keep the sheet dry and 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. Rain causes the square loops of the sheet to stick 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. You can drink this water directly. If one is storing rainwater in other ways and it is likely to become sterilized. The solar pasteurization method can sterilize it. 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 make flood safe drinking water can be used without flooding. In particular, where arsenic is a problem, these technologies can provide a simple solution. According to a British Geological Survey report, there is arsenic in water from 70 feet to 300 feet deep in Bangladesh. Water from rivers, streams, canals, and ponds comes from rainwater, 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. 

In the absence of 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. People can also sterilize contaminated and undrinkable water using the above technology.

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