Near every self-respecting village house there is always a tub in which rainwater is collected. And more recently, every woman knew for sure that in order to preserve the beauty of her hair and face, you need to wash and rinse your hair with rainwater. Because it is the best and purest. Is it really? Let’s try to figure it out together with MedAboutMe.
It is difficult to say what exactly has given rainwater its reputation. Perhaps the fact that it falls from the sky, and heaven is a symbol of purity and holiness. The gods live in the heavens, and the rain falling from the sky seems to carry particles of divine grace in its drops.
Or maybe the rainwater was really clean, especially in comparison with dirty puddles on the ground, with the water of stagnant lakes or ponds. Yes, and many wells too …
In general, our ancestors, who endowed rainwater with a set of some special properties, can be understood. Do contemporaries have reason to consider rainwater the best in quality? So much so that it is specially collected during showers, so that later it can be used for washing, rinsing hair, and even for drinking?
The first thing that comes to mind is that the modern environment is very different from the conditions in which our ancestors lived. We have transport with its emissions, we have industry, including those with harmful emissions. The climate — and that does not stand up and begins to change convulsively. And it is unlikely that the same pure water falls from heaven today as it did a century or two ago.
In fact, everything is more complicated. To understand this issue, you need to understand what can affect the composition of rainwater.
And it’s not just the industry that pollutes the air. For example, forest and steppe fires, dust raised by strong winds, volcanic eruptions and gas emissions from geysers, etc. can “stain” water vapor rising into the sky, etc. All this has always happened, and could successfully pollute rainwater and hundred years ago, and a thousand.
But indeed, modern civilization has become a powerful source of air pollution. Thanks to technological progress, which has given us comfortable cars and airplanes, thousands of different materials and things that appear in factories and factories of the chemical and oil refining industries, the air is successfully and constantly saturated with chemical compounds, particles of toxic substances that react and turn rainwater into a solution with complex and often unsafe composition.
For example, acid rain can fall. This happens if there is a high content of sulfur and nitrogen oxides in the air, which, when interacting with water, form acids — sulfuric, sulfurous, nitric. This is possible, among other things, when rain mixes with smog. Of course, such water should not be collected for any use, especially for washing and drinking.
Rain water after fires is also heavily polluted. As the results of a study conducted by Australian scientists in 2018 showed, such water can only be used for watering plants, and at least livestock can be fed with it only after cleaning.
Microbes don’t sleep
The purity of water in terms of microbiological indicators is also greatly exaggerated. There are quite a lot of bacteria in it, and pathogenic forms are also found. Which is not surprising: after all, each drop flies through a huge amount of air while flying from the cloud to the ground. And absorbs everything that meets on the way.
Chinese researchers have found that bacteria literally thrive in rainwater harvesting systems. Scientists tested samples from such systems for the presence of Pseudomonas aeruginosa (Pseudomonas aeruginosa, an extremely harmful and antibiotic-resistant bacterium), Legionella spp., L. pneumophila, Mycobacterium spp. and M. avium, amoebic microorganisms Acanthamoeba spp. and Vermamoeba vermiformis, and the fecal bacterium Escherichia coli. It turned out that, unlike tap water, all these microbes live and develop perfectly in rainwater and in tanks for collecting and storing it. Moreover, each of the bacteria found its own “favorite” materials: Pseudomonas aeruginosa feels best surrounded by polyvinyl chloride (PVC), Legionella — in tanks and pipes made of stainless steel and PVC, etc. The article was published in 2021 in Water Research.
However, rainwater is cleaner than water from many surface sources if the latter is not purified. That is, in the absence of a water supply system and everything that comes with it — water treatment and water treatment plants, all kinds of filters, etc. — it is better to collect rainwater for use than to collect it in rivers, lakes and streams. A study conducted in 2012 by British scientists confirmed this.
Paul Hunter, epidemiologist, infectious disease specialist
Harvesting rainwater for human consumption is a practice well established in many parts of the world. In this case, the chemical composition of water is usually assessed to a greater extent, but many microorganisms, including opportunistic and pathogenic ones, are also present in rainwater. We analyzed a number of studies and found a number of reports of outbreaks of infectious diseases associated with the consumption of rainwater for food purposes. It was concluded that the use of rainwater, collected under relatively good conditions, was approximately equal to tap water in terms of microbiological safety. And in comparison with the use of water from various natural sources, without special purification and disinfection, it significantly surpasses surface water in quality and carries fewer risks. Therefore, where possible, rainwater harvesting should be encouraged.
Collect or not?
If you follow some rules, then you can and even need to collect rainwater, especially in conditions of lack of water resources.
Of course, the purest, as a rule, is water spilling from the sky where there are no large transport arteries and interchanges, industrial enterprises, and large cities nearby. For example, American scientists studied rainwater collected in Alaska and came to the conclusion that its quality can safely be called high. Indicators of chemical, physical and microbiological contamination did not exceed the norms established by quality standards in 80% of the samples taken. At the same time, the collected rainwater is able to cover up to 40% of the needs of the region.
But even in more “industrial” regions, the quality of rainwater can be quite high if you start collecting it not immediately as soon as it starts to rain, but after a while. The first drops wash out most of the pollution from the air, and then the rain becomes much cleaner.
Of course, for drinking use, such water is still not recommended. But you can use it for other household needs.
Read about the quality of tap water we are accustomed to in the article “Tap Water: Safe or Not?”.