Rainwater Facts and Misconceptions

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.

heavenly moisture

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?

Water purity

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.

Expert com­ment

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?”.