How to Purify Water With Sunlight: Tips & Tricks for Sun Drinking with H2O (Multi-Methods)

Sunlight is a natural purifier of water. But this only works if the water has been exposed to sunlight for some time.

The UV rays from the sun can break down harmful chemicals, such as chlorine and chloramine, which are used in drinking water treatment plants.

Though it seems counter-intuitive, sunlight can be used to purify water. That's right—water can be purified by exposing it to sunlight.

A great deal of the world's water supply is highly contaminated with microbes and parasites that cause diarrhea and other illnesses. What if there were a way to turn the sun into a natural purifier?

It turns out that when water stands in clear containers for at least six hours in direct sunlight, it becomes clear. Water is contacted with molecular oxygen and hydroxyl radicals in the reactants in a container without mixing or boiling.

The following are some tips and techniques to make sure you get the most out of your water purification system:

  • Make sure your bottles have been exposed to full sunshine for 6+ hours before use. If possible, store bottled water in an area with access to plenty of light all day long.
  • Use only clean glass bottles. When plastic is used, chemicals can leach into the water. 
  • Don't drink directly from the tap. Instead, fill up a large jug, then pour the contents back into your bottles once they've had enough exposure to sunlight.
  • The air inside the bottle would dilute the ozone molecules produced during the Fenton reaction. 
  • Keep your bottles away from heat sources like stoves, ovens, etc., as these might alter their chemical composition. 
  • Store your bottles upright so that air doesn't enter the bottle through its opening. 
  • Avoid using plastic bags or caps while storing your bottles. These materials absorb UV rays and reduce the amount of sunlight available to your water.
  • Lastly, remember to always wash your hands after handling dirty water.
  • And finally, enjoy your new filtered water!

Table of Contents

How To Purify Water Using The Sun

When you clean your dishes, you should use freshwater because dirty water can carry bacteria. Running water is the most effective method for washing dishes. Be careful not to let dirty water stand for too long; avoid sewage odors in your home, and stay away from feces.

Water cannot contain chemicals that would harm the plants. The antimicrobial product must have both antibacterial and antifungal components to be effective.

Pour the water into multiple layers of cloth until there are no visible contaminants. Once you've filtered out the sediment from the top layer, leave the rest to settle at the bottom for now. Because clouds prevent most of the sun's light from reaching the ocean, plankton won't be able to thrive.

You can't store liquids in plastic containers for a long time because they leach chemicals harmful to humans. You'll want to check for any damage before buying these items. PET bottles tend to be better than glass bottles for storing liquids like juice. On the backside of the bottle, look for the recycling symbol 1 followed by another number (e.g., 9).

In the summer, colored plastics and glasses won't block enough sun rays from reaching your skin. Some drinks may even prevent UV rays from reaching your eyes entirely.

If you want to fill two-thirds of your bottle with water and then shake them for twenty to thirty seconds, go ahead. But if you don't get rid of bacteria from your body, use an antibacterial soap such as Listerine® Regular Strength Antibacterial Soap. After doing so, fill up the rest of the bottle with water. Place them in direct sunlight for at least an hour daily. Don't give them any reason to stand them up. For the UV light from the sun to reach its full potential, laying these out, so they face up helps maximize their exposure to sunlight.

If possible, place the bottles on a reflective surface such as aluminum foil to maximize their UV exposure.

There may be some white clouds scattered here and there, but mostly blue skies will suffice. Even though clouds cover most of the sky, there may be some clear skies at times. If so, it will take two days for the water to become pure again. Whether it's cold outside or hot inside, long-term sun exposure will protect the skin. When there is any doubt about weather conditions, adding an extra day may be a good idea.

Studies show that BPA-free plastics for baby bottles contain so few toxins that they do not pose any health risks at all.

SODIS for Drinking Water by Dr. John Gulliver provides more information on solar disinfection (SODIS).

Water PASTEURIZATION INDICATORs determine when water is safe to drink.

How to Purify Water with the Power of the Sun: A Step-by-Step Guide

Water is essential for our survival. However, the number of people who do not have access to clean water reaches over 780 million. Hence, this is considered a major global health risk. This is why it is crucial to purify water before drinking it or cooking with it.

Purifying water can be done by using different methods, but some are more effective than others. Among the most popular methods of removing microorganisms from water is solar purification, which uses sunlight.

Step 1: Remove Obstructions to Sunlight

To make water safe, it must be able to be filtered and then disinfected. As a first step, it is important to eliminate any obstructions that may be in the way of the sunlight.

  • Remove any obstructions that may impede exposure of the water to sunlight for a long enough period. These include leaves, twigs, sticks, etc. You should try to keep these items out of the path of the light rays coming from the sun.
  • Make sure that the water's surface does not get covered up when collecting the water. It's best to collect the water directly into containers rather than letting it flow through pipes.
  • Avoid placing objects near the container holding the water. They could block the sunlight and prevent it from reaching the water.
  • Keep the container away from trees, so they don't absorb too much energy. Trees release carbon dioxide, which makes them good absorbers of CO₂. When CO₂ enters the atmosphere, it causes climate change.
  • Use plastic bottles instead of glass ones since they won't break easily. Glass breaks easily and releases harmful substances like lead into the environment.

Step 2: Position Your Container in Contact with Direct Sunlight

This is the second step.

It is time to put the container in contact with direct sunlight.

You should cover it with a black plastic sheet to protect it from rain, dust, and other particles in the air.

Step 3: Position Your Container in Contact with Direct Sunlight

This is the second step. It is time to put the container in contact with direct sunlight. You should cover it with a black plastic sheet to protect it from rain, dust, and other particles in the air.

Step 4: Wait Until the Light Has Reached Its Peak Strength

The third step involves waiting until the peak strength of the sunlight has been reached. If you wait too early, the water might still contain bacteria even though it looks clear. On the contrary, if you wait too late, the water will lose its clarity due to evaporation.

To determine whether the sunlight has reached its maximum intensity, look at the color of the sky.

Step 5. Position Your Containers in Direct Contact With Direct Sunlight

The third step is to position your containers in direct contact with direct sunlight. By placing your containers near a window or in an open space, you can obtain direct sunlight. If there isn't enough sunlight, you can use artificial lighting such as fluorescent lights. You will, however, need access to power sources to implement this method. This also increases the cost of purifying water.

Step 6: Collect the Water From Your Containers

Collecting the water after it has been exposed to sunlight takes only about 30 minutes. Afterward, pour the collected water into another container. The process of pouring the water into another container helps remove impurities from the first one.

Step 7: Repeat Steps 1-4 For Every Day That Passes

Repeat steps 1-4 every day that passes. To ensure that the water remains clean throughout the year, you must repeat the entire procedure each month.

If you live in areas where rainfall occurs frequently, you shouldn't worry about performing all five steps daily. Instead, follow steps 1 through 4 once per week.

If you live in places where precipitation doesn't occur often, you may want to consider performing these steps more than once per week.

Step 8: Store the Cleaned Water for Drinking Or Cooking

After collecting the purified water, store it in a bottle or jar. Ensure that the storage area is well ventilated because storing the water inside a closed room could cause mold growth. When stored properly, the water will remain fresh for up to six months.

5 Best Ways of Purifying Water Using Sunlight

Purifying water is essential for human life. We can't guarantee that chemical-based products will always be available, so we cannot rely on them. We must find alternative ways of purifying water by using natural resources, and one such resource is sunlight.

Here are the five best ways of purifying water using sunlight and its benefits.

1. Solar Distillation System: 

This type of system uses the sun's energy to boil water and separate any impurities in the water. Instead of releasing steam, the water vaporizes and rises to the skies when heated to boiling point. Evaporating hot water results in purer water below.

2. Photolysis Method: 

Ultraviolet light breaks organic compounds into smaller pieces known as radicals in polluted waters. Then, when exposed to oxygen, these radicals combine to form harmless carbon dioxide gas.

3. Ozone Generator: 

An ozone generator produces an unstable molecule known as ozonide. It has been proven that ozonides kill microorganisms better than chlorine does.

4. Reverse osmosis: 

RO systems remove dissolved solids from contaminated water. They work by forcing water under high pressure through membranes made up of semi-permeable material. The membrane allows certain types of ions to pass through but prevents others.

5. Ultraviolet Light Treatment: 

This treatment involves exposing water to ultraviolet radiation.

Limitations of sunlight water disinfection

One of the limitations of sunlight water disinfection is that it takes a long for pathogens to die off. The length of time required for this process depends on the concentration and temperature levels. In general, sunlight disinfection works best at lower concentrations and cooler temperatures.

Heavy metal removal, such as mercury and lead, is another limitation of sunlight water disinfection. These contaminants cannot be destroyed with UV radiation alone. They must also be removed using chemical methods.

How to Purify Drinking Water with Solar Technology?

Those who prefer to purify their drinking water naturally can consider solar water purifiers. From being eco-friendly to being cost-effective, they have a range of advantages.

Sustainable drinking water solutions like solar water purifiers have been around for decades. They have been reinvented as a greener and cheaper alternative in recent years.

Solar water purifiers still function using the same basic principles, so they are not new or revolutionary. What has changed is that these devices are now far more affordable to install at home than before. As a result, they are an even better choice if you're looking for something green and affordable!

Benefits of Solar Water Purification

Keep water under sunlight has many benefits. The benefits are included herewith:

  • UVA rays may activate the oxygen into water, form hydrogen peroxide and oxygen free radicals that kill pathogens.
  • The merit of keeping the bottle under sunlight is to speed up the disinfection progress.
  • The process is inexpensive and portable and only needs plastic bottles and sunlight.
  • The rays of UVA destroy the cell structure of pathogens.

Cautions and Limitations

If water is not sun exposed properly, it is not safe to drink. This type of water may cause illness. For overcast weather, if the sunlight is not strong enough, a longer time of exposure is essential. Then you need to consider the following issues:

Bottle material

Bottle material

PVC materials or some glass resist ultraviolet rays from reaching to water. So commonly used a bottle that is made of PET are suggested. The handling of the bottle is more convenient in the case of PET bottles. UVB rays, Polycarbonate blocks all UVA are not suggested to use.

A bottle having no color is suggested then the colored bottles. Suppose the green of some lime soda or lemon pop bottles.

Aging of plastic bottles

SODIS efficiency relies on the physical condition of the plastic bottle, up to scratches or the other sign of wear lessening the efficiency of SODIS. Old, heavily scratched and blind bottles need to replace.

Shape of containers

Shape of containers

The intensity of the UV radiation becomes lessen with the increase of water depth. If the depth of water is 10 cm and turbidity of 26 NTU, UV-A radiation reduces to 50%. Soft PET bottles are found easily and most appreciating for SODIS application.


Sunlight makes highly reactive forms of oxygen over water. The reactive molecules help to take part in the process of microorganisms. Under the general condition, water holds sufficient oxygen and need not be created before the application of SODIS.

Leaching of bottle material

Leaching of bottle material

There are some questions in people mind whether plastic drinking water containers remove toxic components or chemical from water or not. The Swiss Federal Laboratories for Materials Testing and Research tested diffusions of phthalates or adipates from reused and new PET bottles during solar exposure.

The result found in water after 17 hours is 60 degrees C; water is far below than WHO standard of drinking water. At the same way, the concentration of adipate and phthalate is higher in tap water.

Think about the PET bottles of water. A report published by the researchers from the University of Heidelberg released of antimony from the PET bottles for mineral and soft drinks stored for few months in the supermarket.

The standard of water is below the standard of WHO and guideline for antimony concentration for drinking water. So, SODIS water is not kept over extended periods inside bottles.

Regrowth of bacteria

If you remove it from sunlight, the rest of bacteria will reproduce again in the dark. This is the outcome of a study in 2010 that just ten parts per million of hydrogen peroxide is very active to prevent the regrowth of wild Salmonella.

Toxic chemicals

Solar water disinfection fails to remove toxic chemicals which are found in the water like factory waste.

Want to know more, click here to know how to purifying water.

Frequently Asked Questions (FAQs) about How to Purify Water Using The Sun

1. Does the Sun's Current Strength Matter When it Comes to Water Purification?

One day, we might not have to boil water to make it drinkable. That is because sunlight can be used to purify water and make it safe for consumption.

UV photons can kill bacteria and viruses, while the sun's rays can break down organic compounds in water. However, this still doesn't negate the need to filter the water before you drink it. You don't want to get sick after drinking something that was purified using solar power.

The sun can help us purify our water, even though its strength isn't enough to disinfect water completely.

2. How Much Sunlight is Required to Render Unsafe Drinking Water Safe?

Solar energy is needed to purify drinking water depending on its physical and chemical properties. Pollutants like dust or smoke particles can also contaminate sunlight.

Several studies suggest that sunlight is necessary to make drinking water safe. If you live in an area with sunshine for six hours a day, your water only needs to be boiled for 15 minutes. You will have to use electricity or firewood if sunlight isn't available during those six hours.

3. What is the solar energy needed to purify water?

The boiling point of pure ethanol at sea level is 78.3 degrees Celsius. Therefore, it would require a significant amount of solar energy to purify water with pure ethanol.

The boiling point of pure ethanol at sea level is 78.3 degrees Celsius. The higher the temperature, the more intense the heat, and the larger the amount of heat required to distill alcohol, which is how you can purify water with heat.

4. How Much Time Will Sunlight Purification Take for the Process to Finish?

The filtering process is dependent on how much water you need to filter and how long you leave it to filter.

In general, it takes between two and three hours to fill a single glass of water, 10-20 days for a pond, and 4-6 weeks for an artificial lake.

5. Can a DIY Solar Powered Water Filter Save Lives in Disaster Areas?

There are more than 1 billion people without access to clean drinking water. Worldwide, the population afflicted with water-borne illnesses is at a high of 783 million people. In disaster areas, this number is much higher.

Solar-powered potable drinking water systems can assist those who cannot access water through traditional methods. Providing clean drinking and bathing water, this system improves the quality of life for those in need.

6. When Should You Add Salt to Your Solar Disinfection Process?

Saltwater treatment involves heating the water to about 50°C to dissolve all the salt particles. This process will kill any bacteria in the water.

In solar disinfection, salt helps increase the contact time between UV radiation and microorganisms. It also helps to prevent organic growths on equipment surfaces.

The salt will enhance UV rays' reaction with microorganisms, thus increasing their contact time. Moreover, the high salt content of seawater can prevent organic growth from developing on equipment, which could cause rusting or corrosion that could decrease efficiency over time.

7. How to Test if Your Solar Filtration System is Working Properly

Solar-powered filters are an efficient way of filtering water. They have been used for a long time, but there is still confusion about how these systems work. 

We will then introduce you to the best solar filter that we could find on the market today and talk about its features.

8. What to do If Your Solar Filtration System Has a Problem?

Your solar filtration system is passive if no pump is used. There is a gravity flow from the source to the storage vessel, and there are no moving parts in this process.

Passive solar water filtration systems are not complicated to build or maintain. However, many troubleshooting steps can be taken before it becomes too complicated.

This section will outline the four most common problems in a passive solar water filtration system and how to retrieve them.

9. When can you drink from the solar-water purifier?

You can drink from the solar-water purifier on a sunny day. If your home has windows facing south, you should be able to use the purified water without worrying about cloudy weather conditions.

10. What is sunlight disinfection of water?

Water is disinfected with ultraviolet light by causing DNA damage to microorganisms. Drinking water is improved by this process, as well as diseases caused by microorganisms are prevented. Solar energy is transformed into heat when it reaches the earth's surface. Some of the heat from the sun reaches the ground and heats the air around us.

During daylight hours, the average global temperature rises above the freezing point. At night, however, the amount of direct sunlight decreases dramatically. As a result, temperatures drop below zero degrees Celsius.

11. How effective is sunlight water disinfection?

However, sunlight water disinfection does have some limitations. The effectiveness of natural sunlight varies depending on the time of day and weather. It may take several days for sunlight to kill all bacteria present in contaminated water.

The intensity of sunlight varies throughout the year. The intensity of the sun drops considerably in winter because fewer hours pass through each day. On the other hand, summertime brings longer periods of bright sunlight.

The full spectrum of visible light must reach the water being treated for sunlight disinfection. Clouds block out much of the sunlight needed to treat water effectively.

12. Is sunlight water disinfection safe?

Yes! There are no known health risks associated with sunlight water disinfection. You might want to install a backup power source if you live near or work in an area prone to wildfires.

13. Which water is best for sunlight disinfection?

The best type of water for sunlight disinfection is distilled, so it would be best to use distilled water to get the most efficient results. Distilled water has a high mineral content, which helps to kill bacteria. If your tap water contains minerals, then you should filter it before treating it with sunlight. You could also add more salt to make sure that any remaining organisms will not survive.

14. What about cloudy skies?

Clouds do affect how well sunlight disinfection works. Cloudy skies reduce the amount of solar radiation reaching the ground. Therefore, less heat is generated from the sun's rays striking the ground. Consequently, the overall efficiency of sunlight disinfection declines.

15. How do I disinfect cloudy water?

To disinfect cloudy water, one must first heat the water to a boil and then add 1 teaspoon of unscented bleach. The mixture should stand for three minutes, then pour it through a strainer. It should cool before being poured into a water container. This procedure kills 99% of harmful microorganisms.

16. Can sunlight clean water?

It is probably not, but it is worth noting that sunlight can kill bacteria and other harmful microorganisms. Additionally, ultraviolet light can break down pollutants in water. It does require some energy, though.

For example, when exposed to direct sunlight, chlorine gas breaks down into oxygen and hydrogen chloride. Hydrogen peroxide is another compound formed by exposure to sunlight. H2O2 is used to purify drinking water.

17. How does sunlight heat water?

Sunlight is a major source of energy that heats water in the planet's atmosphere. When the sun's rays hit the earth, they are converted to heat and travel through the ground to the ocean's depths.

 Hydrogen and oxygen are split from water molecules at this point, which plants can then use for photosynthesis. 

When these gases come back up to the surface, they combine again to form liquid water. As mentioned earlier, sunlight also causes the formation of ozone and hydroxyl radicals. OH destroys organic compounds while ozone protects us from certain types of cancer.

18. Why doesn't my water smell after being treated with sunlight?

As water flows from the faucet, it usually smells bad because of all the different chemicals present in our bodies.

19. Is sunlight safe enough to drink?

Yes! Drinking water purified using sunlight is perfectly fine.

20. What happens when you put water in sunlight?

Many people think that putting water in sunlight will make it evaporate and turn into vapor. This is not true because the sun's heat converts the liquid to a gas and then back again.

Nonetheless, if your water contains impurities such as iron or manganese, those elements may precipitate. If so, the resulting solid particles could clog pipes and cause problems downstream.

21. How long does it take for sunlight to sterilize water?

It takes about two hours for sunlight to sterilize water. During this period, the amount of UV-B radiation decreases at a rate of 0.5% every minute. After 2 hours, only 1/10th of the original intensity remains.

22. How long does it take for sunlight to kill bacteria in the water?

The process of sunlight exposure is known to kill bacteria in water. According to research, sunlight exposure kills most bacteria in a liter of water in four hours.                               

23. Does sunlight affect other things besides just killing germs?

In general, yes. Ultraviolet radiation has been shown to have effects beyond simply destroying microorganisms. Some studies suggest that UV radiation affects human health negatively.

Specifically, UV radiation damages DNA within cells, causing mutations and possibly causing skin cancer. Scientists argue that UV radiation reduces cholesterol levels and prevents heart disease. Still, others claim that UV radiation reduces inflammation.

SOLAR DISINFECTION - SODIS - How To Purify Water In A Bottle With The Sun

Statistics of Purify Water Using The Sun

Based on the research results:

  • The water will take 2 days to purify if the sky is more than 50% cloudy.
  • East Lombok District, Indonesia, has access to water for 50 percent of the population and sanitation for 38 percent.
  • Solar disinfection of drinking water has reduced bacterial contamination by 97 percent as a result. 
  • More than 70 percent of users had less diarrhea.
  • There is a remarkable 5-Nine, or 99.999 percent, the effectiveness of terminating harmful bacteria. 
  • At a depth of 10 mm (about 0.5 inches), UV-A loses 50% of its effectiveness in moderately cloudy water, but it only loses 25% of its efficacy in clear water. 
  • In areas of sunshine (less than 50% cloud cover), UV-A is most effective. 
  • There is little to no rain when it is cloudy (50-100% cloud cover). 
  • These regions receive high solar radiation, have little cloud cover, and directly receive over 90% of the sunlight.
  • If the letters cannot be read, the water is likely to be turbid, and it needs to be pretreated.


Water is essential for life. Unfortunately, most people don't drink enough pure drinking water. They rely instead on tap water, bottled water, or soft drinks. These types of beverages aren't good for our health.

Fortunately, we now know how to make safe drinking water using natural methods. We've learned how to purify water using sunlight.

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