Solar Radiation Effects on Drinking Water

In this brief article, we’ll talk about solar radiation effects on drinking water.

We’ll also dive into water bottles that are sitting in the sun for too long, the several impacts of sunlight hitting the water, solar disinfection, and answering some commonly asked questions at the end. Let’s jump into it!

Is it safe to consume water from a bottle sitting in the sun?

Let’s say that it’s a hot summer day, and you’re dehydrated—you need some cool, refreshing water. The only water around you is from a water bottle that’s been sitting in the sun, maybe in a car or in a backpack while you’re hiking. Is it safe to drink from that water bottle?

Water doesn’t “expire” for a while—usually, water can generally be stored for up to six months. Even though the water doesn’t expire or go bad, it’s usually the container, solar radiation, and other contaminants within the water that makes it unsafe to drink.

The expiration date that you’ll see on water bottles usually refers to the expiration date of the plastic rather than the water.

With that being said, the plastic that water bottles are made of is called PET plastic. When warmed up by heat from your car or the sun, PET plastic can release chemicals into the water, which is why chilled bottled water tastes different than lukewarm bottled water.

Many studies have proven that water bottles left overnight or during the day inside of a car didn’t release enough chemicals to cause any severe effects on humans.

The bottom line is that it isn’t unsafe to drink from that water bottle that’s been sitting in your car for a day, even though it won’t taste refreshing, but don’t make it a habit! Leave these water bottles to be used as a last resort.

Top Solar Radiation Effects

There are many impacts of solar radiation that affect other properties on Earth, whether on a large or small scale. For example, when the rays from the sun hit the water on Earth, some of the measured effects are:

  • Evaporation – Simply, when sun rays hit the water on Earth, the water evaporates to the relative top in the form of tiny, invisible droplets.
  • Greenhouse effect – When the sun hits water or land on Earth, the heat produced bounces off of Earth’s surface, but it becomes almost trapped in the atmosphere—some of the rays are reflected into space, but some stay inside the atmosphere and heat the climate over time.
  • Ozone layer – The ozone layer absorbs solar ultra-violet radiation and affects how much of the sun’s heat is bounced back into space. The ozone layer protects us from the excessiveness of UV radiation which can cause sunburn, skin cancer, and eye damage.
  • Aerosols – Inside the atmosphere, there are small, suspended solid and liquid particles of dust that float around—they are usually the results of air pollutants, rising sand, forest fires, vehicle exhausts, and much more. As the sunlight hits these pollutants, the rays from the sun can scatter or be absorbed, which causes reflectivity, haze events, and additional heating in the atmosphere.
  • Albedo effect – This effect is similar to the greenhouse effect, but albedo is more about the ability of a surface to reflect sunlight and solar radiation—snow and ice, for example, have a high albedo. The more snow and ice in the Arctic and Antarctica melt, the more dark surfaces; hence, the climate becomes warmer.
  • Water cycle – Sunlight hitting the water on Earth is vital for our ecosystems. As sunlight hits the water and the water evaporates, rain/snow occurs. Precipitation is essential for all living things on Earth, and without the water cycle, life on Earth wouldn’t exist.

Solar Disinfection

Solar disinfection, also known as SODIS, is a portable water purification method that uses solar power to make contaminated water safe to drink. In short, there are many ways to turn dirty water into drinkable water using the Sun’s energy.

Using the invention of solar stills, water from all kinds of sources can be made drinkable. A solar still is a mechanism that allows water to evaporate and be collected as drinkable freshwater.

For example, take a giant tub of water. Over the tub of water, place a glass sheet at an angle, and at the low end of the sloped glass sheet, make a connection to an empty tank. As the sunlight hits the giant tub of water, the water is slowly evaporated and floats to the top, where it attaches itself to the glass sheet.

Referenced WaterResearch

As more water is collected at the top, instead of falling back into the giant tub, it will roll down the glass sheet, where it will go to the empty tank. This is a slow process, but over time, you can have a lot of drinkable freshwaters.

Solar stills don’t need to be complex or large; solar stills are made using a transparent plastic sheet and a water bottle in the ground that works just as well. Just be careful—this method should be used for emergencies only as there are many water sources out there that are polluted with fuel and other contaminants that are unable to be filtered through evaporation.

Water In Nature

Solar radiation can cause plastic to release chemicals inside the water. Still, in different, safer material like glass, it is a lot safer—solar radiation itself doesn’t cause any issues besides evaporation.

For water found outside of your home may seem safe since it isn’t inside of a plastic container, but there are other harmful contaminants inside the water that might make it undrinkable.

Don’t worry—water from sources outside the home can be treated to kill harmful germs.

Ways to use solar radiation to filter water.

For example, if you grab an empty water bottle, fill it up with unfiltered water, and leave it under the sun for a few hours, you’ll see water droplets form on top of the water bottle. Those droplets are water droplets that have evaporated and don’t contain germs.

Be careful, though—this method should be used only in emergencies, and the water must be from any of these sources:

  • Collected rainwater
  • Streams, rivers, and other moving bodies of water
  • Ponds and clear lakes
  • Natural springs

Do NOT use water that has been contaminated by fuel or toxic chemicals. If the water has an unusual odor or color, the water cannot be made safe, so you must find a different source of water for yourself.

Water in developing countries with poverty

Due to a water-related disease, there is one death out of every five deaths under the age of 5 worldwide—about 80% of illnesses are linked to insufficient water and sanitation conditions, according to a report done by The Water Project.

Besides death, the lack of access to water leads to many other health conditions that affect the workforce in general and cause workers to miss work—this impact leads to poverty. Communities affected by natural disasters or artificial are more resilient if they have access to safe water and sanitation.

Groups like WHO and UNICEF have stepped up to invest in a program known as the Global Water and Sanitation Hygiene (WASH) which promises one of the highest rates of return of any development relating to water, hygiene, and poverty. The advantage is that every $1 spent yields anywhere from $3 to $34 in economic return, but the disadvantage is that the lack of WASH can cost up to 5% of a country’s GDP.

Common FAQ

Are water vapors created from solar radiation?

Yes, water vapors are created from solar radiation, but it isn’t the only way water vapors are produced. Another common way to generate water vapors is through boiling water. When water boils, water vapors in the form of steam are created—the difference between water vapors and steam is that steam is more visible and created through heat.

Can solar radiation kill bacteria in the water? If so, how?

Yes, solar radiation kills bacteria in the water. Solar disinfection, SODIS, uses the sun’s ultraviolet rays to kill bacteria and microorganisms in the water. When a sealed, clear water container is exposed to sunlight, over time, the UV radiation destroys bacterial, viral, and parasitic pathogens, allowing dirty water to be drinkable.

Be careful, though—solar disinfection will destroy bacteria, but it won’t make water with fuel, radioactive material, or gasoline drinkable or safe.

How is Earth’s solar radiation measured?

Earth’s solar radiation can be measured as the total radiation over a horizontal surface; a standard method measures the amount of energy that comes through solar panels.

The amount of electricity generated through a solar panel can determine how much solar radiation there is on the surface of the solar panel.

For example, if there are 60 kiloWatt-hours of electricity generated through a 3-meter by 5-meter solar panel, you would simply take 60 kiloWatt-hours divided by the area (15 meters squared) would give you the result of 4 kiloWatt-hours per square meter.

Direct estimates of solar energy may also be expressed as the Wattage over the area as Watts per meter squared.

How does solar radiation happen?

Solar radiation, or evaporation for water, happens when a liquid becomes a gas; the molecules within the water move and vibrate so quickly when heated that they escape into the atmosphere as molecules of invisible water vapors.

This can happen from boiling the water in the form of steam or from the sun hitting water inside a water container.

The evaporation process makes it super convenient for solar stills to produce freshwater from most water sources.

Key Takeaways

  • You can drink from a water bottle that’s left in your car for a few hours, maybe even overnight, but don’t make it a habit.
  • Water left in sunlight is only harmful because of the plastic water bottle.
  • Solar radiation doesn’t cause harmful effects to water; in fact, it takes dangerous stuff away.
  • Solar stills are a great way to gain access to fresh water in nature.
  • Do NOT drink from a water source that seems like it has toxic pollutants.

For more information on drinking water, the CDC website has all that you need for what to do and where to go for water sources for solar disinfection. Otherwise, to help out to developing nations and helping out with WASH, go to the UNICEF website or the WHO website for more information on donations and how you can help

Ying Xu

Graduated from the University of Kansas with an Aerospace Engineering degree & served 4 years as an US Air Force officer. Experienced with basic survival skills, weapon system security,  technical disaster recovery, and system troubleshooting

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