DANGER number one:

Rainwater is normally very acidic.....read why.

DANGER number two:

Acidic rainwater can leach metal from your roof/spouting.

DANGER number three:

Rainwater is normally distilled water.....read why a danger.

DANGER number four:

Rainwater includes pollutants from earth bound activity.


1. Rainwater is normally very acidic

By the nature of the role rainwater has, once it lands on the surface of earth, it simply HAS TO BE acidic. Its average pH is about 5.6. 

It has several roles, one of which is to seep into the soil and make its way as 'recharge waters' for groundwater replacement --- and eventually (maybe hundreds of years later) into aquifers. To travel underground and progress, rain water sometimes has to be able to 'burrow' its way through other materials like limestone. To achieve this rain water is more acidic than , for example, limestone. Some other rains grind their way through soils, forming streams and later rivers. Sure they do this in part by their velocity and force, but by being acid this helps also this journey of rain water.

One assessment of the difference between acidic v alkaline is the pH measurement system.

The term pH is a measure of the concentration of hydrogen ions in a diluted solution. It can range from 0 to 14, with 7 denoting a neutral value.

Acidic water has a pH below 7; alkaline water, above 7. Some health effects of drinking water depends on the pH of that water. When one sees changes inside their electric jug, this can be due to extremes in pH of water used and/or due to the softness of hardness of water.

Because a logarithm scale is used to calculate pH, this means that a pH of 6.5 is 5 TIMES more acidic than a pH of 7. It is not 0.5 times different....it is the much greater 5 x different.

For those still a skeptic, perhaps because they have been drinking rain water for some years....another matter is tabled. Remember cigarette smoking was considered fine for decades, and its negative effects on some human bodies came to surface sometimes 40 years after smoking began. Then those lagged effects could be horrific,

For those who do not believe rain water is acidic we refer you to the Universities blog debate/trail, included at the lower section of this page....which suggests rain water pH is normally between 4.2 and 6.7, with an average pH of about 5.6, (and in a few cases higher due to environmental influences, not natural pH of rainwater; rain water is usually about 5.6/5.7 ).

For those of our readers who do not believe everyday consumption of acid water may be potentially damaging for your health --- consider the fact that our blood's pH is about 7.35 and our blood is about 90% water.

Aquatic wildlife also suffer from the effects of pH extremes. Fish die-off occurs when pH levels in water they live in dip below 4.5 or rise above 10, according to a report by the Northeastern Regional Aquaculture Center at the University of Maryland, USA.  

Also watch a few of the videos in our Cinema, which refer to suggested healthy drinking water.

Many City Councils add lime or some other alkalinising powder to drinking water to lift pH before sending it to taps...but then who really wants to drink lime?

The U.S. Environmental Protection Agency, which classifies pH as a secondary drinking water standard, recommends a pH between 6.5 and 8.5 for drinking water. NZ Ministry of Health recommended a pH between 7 and 8.5.  

 http://www.renewedlivinginc.com/healthy-drinking-water-alkaline-water/       ON that web site there is a WARNING: 'The intake of excessive amounts of acidic water can cause your body to work overtime with the threat of weak bones, the development of an illness or obesity..... The absence of alkalizing minerals in our water draws the alkalizing minerals out of our bones and teeth'.  

Dr. Otto Heinrich Warburg, a biochemist and 1931 Nobel Prize winner for his work with cancer cells and oxygenation told us about the connection between acidic water and disease long ago. He wrote:

“Diseased tissues are acidic, whereas healthy tissues are alkaline. Water contains H+ and OH- ions. If there is an excess of H+, it is acidic. If there is an excess of OH- ions, then it is alkaline.”

2. Acidic rainwater can leach metal from your roof/spouting

The fact rainwater IS acidic, means it can scrape off tiny amounts of metals from your roof and/or spouting or downpipes. This might include the very dangerous lead, if lead nails form a part of the roof covering or the spouting or downpipes. 

What ever the roof is made of, having tiny amounts in every day drinking water is not to be encouraged.

Acidic rain water can also negatively affect plumbing systems. The nonprofit Water Systems Council warns that  toxic metals skimmed by acid water into the water itself, can can include substances such as lead. The New York State Department of Health explains that lead exposure can lead to a host of neurological and reproductive problems, such as seizures, hearing loss and miscarriages.

See http://www.livestrong.com/article/214475-health-effects-of-ph-on-drinking-water/

If acidic water can leach the interior lining of pipes, what can it do to interior of the body?

NZ's Watercare advises on their web site that one of reasons they add lime to drinking water is to lift pH, so the water does not leach out interior of pipes the water is traveling in to homes!

3. Rainwater is normally distilled water

Of course rain water is distilled by the process of the hyrologic cycle...see diagram of this HERE.

The surface water evaporates from the earth's surface, and in doing so creates a distilled water in the sky, a water devoid of earth's natural minerals.

Aside from the non-sought after airborne polluting particles (e.g. poisonous exhaust fumes from cars, trucks, aeroplanes etc) which can intermingle with rain, the rain itself is distilled water.

Here are two commentaries of possible dangers linked to medium-term drinking of distilled water (see more on the audio and videos of these health professionals in our Cinema pages):

  • All water found in nature has some dissolved trace minerals. Distilled water is a man made water which has none. Lawrence Wilson BSc writes:

“Distilled water acts as a chelator in the body. In our experience with many clients this is a very serious problem. Distillation (as with reverse osmosis) creates a "hungry" water.” Distilled water is devoid of minerals/TDS. It can attract to itself the minerals it has had taken from it - then leach these minerals from us.

  • Dr J Mercola writes:

"In choosing the right type of water for you and your family, you want to aim for pH balance. Distilled water is too acidic and alkaline water is too alkaline. The ideal pH of your water should be between 6.5 to 7.5, which is neutral."

4.  Rainwater includes pollutants from earth bound activity

Near everyone has heard the expression of 'acid rain'.

This normally does not 'just' refer to the fact that rain water is naturally acidic --- most likely it refers to the array of human produced pollutants, which become airborne and combine with rain, then shower an extreme acidity on the earths surface and on the many things growing/living thereon (including humans, animals, birds, trees, etc). 

Human induced airborne polluting particles include the poisonous exhaust fumes from cars, trucks, aeroplanes etc, the waste smoke and other particles from industrial activities, smoke from home fireplaces, and much more; not to be dismissed of course being the radiation poisons from Chernobyl and Fukishima. Then there are the natural hazards, like forest fires, volcanoes and the like. Each can result in particular substances intermingling with rain clouds and falling with rain. In parts of Europe acid rain is held responsible for deaths of trees in forests. 

One remarkable situation is that acid rains which includes these human induced pollutants rarely fall over the same area responsible for the originating air pollution. The winds in the sky ensure this. By example,much of the air pollution from cars and trucks operating as Auckland City traffic, actually moves north east with the prevailing southerly winds, and then falls more likely over those holidaying or resident on the Whangaparoa Peninsula!

These air borne pollutants are not something to be readily drunk with rain water. Filters would be needed if one is consuming rain water --- and then the added challenge of what filter and the possible damage it might bring to the water are all a part of further considerations.

p H

While the average pH of blood is 7.35, the average pH of cells is 7-7.3.

The blood pH only varies marginally from 7.35  in a healthy individual.

Large changes in blood or cell pH can be life threatening.

Although there is great variation in pH between the fluids in the body, there is little variation within each system.

In the body, the pH of cells and extra-cellular fluids can vary from pH 8 in pancreatic fluid to pH 1 in stomach acids, but as noted above the average pH of cells is 7-7.3.

How does the body maintain a constant blood pH?

The body uses a buffer system to withstand changes in pH. Buffers are made up of a mixture of a weak acid with its conjugate base or a weak base with its conjugate acid.

When acids or base are added to a solution such as water, the pH changes.

The human manged or controlled addition of an acid or base to a solution  e.g. to drinking water) is called a titration. This can artificially change a waters pH. See more HERE.




Q Is rainwater with a pH of 6.5 normal during a hazy period?

Question from: Chin Yik Lin · Universiti Malaysia Sabah (UMS)

I've been sampling rainwater since last week to study its pH values after a long, dry, and hazy period (~60 days no rain). But the results don't seem to make any sense. 
Here is my experiment:

On the first day of rain after a long drought, I sampled and measured the rainwater pH and surprisingly found that the pH reading is exceptionally high (pH 6.5). Four days later, it rains again and the pH this time is 4.38. On the fifth day, there is more rain and the pH is 4.26. Does anyone know why the pH of the 1st day of rain is less acidic? Thank you very much.

Second response same Q:  Thank you very much for all your helpful comments and great ideas! I just run the rainwater analysis using ICP-MS, measuring dissolved ions and get the results. I think the results supported your explanation to a good extent. Here is the results: 
1st day sample: 2nd day sample: 3rd day sample:
Ca: 1187.72 ppb Ca: 442.42 ppb Ca: 510.10 ppb
K: 329.67 ppb K: 80.69 ppb K: 42.34 ppb
Sr: 3.61 ppb Sr: 1.11 ppb Sr: 0.45 ppb

I will validate the results again (anions and cations) using IC (ion chromatography) next week. Also, I plan to measure total ions in the rainwater and compare with those of dissolved concentration. Hope to get more exciting data! Thank you Professors! It is worth mentioning that my study site is at Kuala Lumpur, Malaysia (where bush fire is common).

 Mar 21, 2014


Zenaida Usagawa · Centro de Estudios Ambientales de Cienfuegos

I want to present you another perspective of problem. If you have a long period without rain, then there is lot of dust in atmosphere. This dust very often is mainly composed by soil particles, particularly in ventilated areas with high calcium content. In this context, carsic dust can neutralize rain acidity. In a dry week on a carsic plain, pH of rain samples of the first minutes can get up to 8.0. This phenomenon depends of local characteristics of site and of the air composition where clouds are formed (local wind systems like breezes, convergence zones). I have monitored rain in a south coastal site, predominant wind from Northeast, and I have found acid rain only with rain from South, from sea. 
My answer is "This pH could be normal".

 Mar 20, 2014

Sanjay Mohanty · University of Pennsylvania

The average pH of rainwater is around 5.7 due to the presence of carbonic acid (carbon dioxide dissolves in water). But the pH of rainwater could vary based on atmospheric conditions. In particular, the sulfuric acid and nitric acid from atmosphere can dissolve in rainwater to lower its pH. These acids are formed in atmospheres from NOx and SO2, which enters atmosphere because of combustion of fossil fuel such as coal in addition to other natural processes (seehttp://www.epa.gov/acidrain/what/)

In summary, a pH lower than 5.7 could mean that the rainwater has more nitric and sulfuric acid. A pH higher than 5.7 (say 6.5) is also not uncommon. All depend on what are being dissolved in rainwater in that given day or the atmospheric conditions (dust, thunderstorm, antecedent climate etc.).

 Mar 20, 2014


Ivo Allegrini · Formerly: National Research Council

Besides alkaline material incorporated in raindrops (soil dust) from contamination, another possible source of rain "alkalinity" may directly come from clouds. Fronts may be such that long range transported air masses can be incorporated into clouds. In Mediterranean sites this is very common since fronts include southerly air masses from Sahara containing calcium-rich particles. In this case, rains may show pH above 7. This effect can be easily seen by looking to evaporating rain drops which leaves reddish fine particles on surfaces. After the development of fronts, southerly air masses are replaced by westerly-northerly air masses and pH drops to a more natural acidic value.

 Mar 21, 2014

Pravin K MUTIYAR · Indian Institute of Technology Delhi

Its normal to have an acidic pH for rain water.

Since you are doing ionic content analysis, you will get the answer for the specific pH (acidic or neutral).

 Mar 21, 2014

J. William Munger · Harvard University

Previous comments have already pointed out the potential for alkaline soil dust or ammonia to neutralize rainwater. If there is a lot of agriculture in the nearby area you could expect high levels of ammonium, otherwise soil dust from bare ground, traffic, and construction activity are good candidates.
If these materials are in the air precipitation will very effectively wash them out, so you will get the result you have observed without having to consider contamination of the sampler.
A point not made yet is that once it has rained a little and wet the nearby soil the source of windblown dust should decrease considerably. The next rainfall will be dominated by the acids from oxidizing SO2 and NO

With the IC analysis you can look at the balance of anions and cations and an excess of cations over the sum of sulfate, nitrate, and chloride will confirm that you have HCO3- and CO3(2-) alkalinity.

The transition from neutral to acidic rainwater is analagous to what I observed in thesis work in the 1980's where rainwater at a site in agricultural/prairie landscape of North Dakota was neutral to slightly alkaline and the rain further east in forested area of Minnesota was acidic down to pH between 4-5.         ( ATMOSPHERIC ENVIRONMENT: 16(7), 1633-1645
DOI: 10.1016/0004-6981(82)90258-X, 1982 )

 Mar 21, 2014

Yadiana León · Centro Nacional de Investigaciones Cientificas

The rain water in equilibrium with atmospheric CO2 should have a pH around 5.6, if we consider the carbonic acid as the sole source of the hydronium ion. However, in some areas of our planet, the pH of rain presents values well below the expected value of 5.6. The main agents causing acidification are the dioxide of sulphur (SO2) and oxides of nitrogen (NOx), and to a lesser extent the ammonia (NH3).

Compounds that modify the pH of rain water comes from natural sources biogenic (compounds from the ocean, tides, etc.), not biogenic (from geothermal energy, combustion, and aerosols from soil and water) and anthropogenic sources that use fossil fuels (industry, transport, home) of each of these acid rain precursors emissions sources, is based on socio-economic activities of each region.These compounds can be transported by wind and deposited on the Earth's surface by gravity in the form of powder, which is technically called as dry deposit.  Answer: My opinion is that this pH could be normal.

 Mar 21, 2014

Virendra Kumar Saxena · National Geophysical Research Institute

Observation was taken at National Geophysical research Hyderabad, during Aug- Sep., 2001, in peak rainy season, observed pH of rain water in 350 samples, and found pH : 6.2 to 6.7 in 62% samples; and 5.6 to 6.1 in 26% ( pH was immediately observed after the rain water collection without any contamination). Non of the sample was found towards alkaline in nature.

 Mar 22, 2014

Hutaf Baker · Al - Albayt University

The higher value of pH may be,the content of the atmospheric CO2 which is a weak acid is small, less than 370 ppm. Now the lowering in the pH is because of the SO2 and NO3 in the atmospher.

 Mar 24, 2014

Richard Artz · National Oceanic and Atmospheric Administration

There are a number of good answers here that have addressed soil dust, agricultural activities, etc. The measured value may or may not be correct. Most of the responses did not cite established sampling protocols, a key consideration for making high quality routine measurements addressed in the WMO Global Atmosphere Watch 2005 guidelines for the collection and analysis of precipitation chemistry samples. See: http://qasac-americas.org/sites/default/files/GAW-Precip%20Chem%20Manual%20No.160.pdf

 Mar 24, 2014

Deljo Davis · University of Utah

Acidic pH is normal in rain water but the ionic contents presented here has more question about the measurement error.

 Mar 24, 2014

Modinah Abdul Raheem · University of Ilorin

Hello Chin, What you have experienced could be due to a localized problem from your sampling point i.e it could be due to the direction of wind that brought about the rain at the point of fall, the type of the pollutant released in to the air which forms the haze differ and depend on activity that causes its release. If the air is loaded by Calcium ions, ammonium ions or sodium ions etc, the rain acidity could be neutralized. Any of this could be the atmospheric scenario at the first time of your sampling.

 Mar 25, 2014

 Mar 25, 2014

The alkalinity is altered by Ca, Mg and K ions. If the region of studies has sources of these elements (e.g. limestone mines), aerosols containing such databases may raise the pH of the rain, especially after long periods of drought. Also the formation of NH4 raises the pH of the rain. A careful study of the chemistry of both wet and dry precipitation, more a study of the chemical composition of the troposphere should answer the question. Be careful with the pH probes and buffers. These must be special to measure pH very diluted, low conductivity water.

 Mar 26, 2014

G. M. Taha · Faculty of Science, Aswan University, Aswan, Egypt

You should study the following:
1- wind speed to decide if the cloud was in the study zone for long time or not.
2- the content of pollution in your zone where it is obvious that there are acidic pollution.
3- I think the cloud of the first sample was in contact with the polluted atmosphere for short time. 
4- the quantity of rain water in the first day was big to the extent to make self dilution to the acidity.

 Mar 26, 2014

Neal Phillip · City University of New York - Bronx

We did research with cloud water at Storm peak Lab in Steamboat Springs Colorado and colected cloud water samples with pH values of 2.0 or less. I think pH is a measurement that has to be done immediately. If you allow the sample to sit evolution of CO2 gas could cause the pH to be higher. So check to see the lag time between sampling and analysis of the three rainwater samples. If they were the same then you might want to do a trajectory analysis to see where the the predominant wind directions was during the three rain events. This will tell you something about the nature of the condensation nuclei and ultimately the pH of the rain water samples.

 Mar 27, 2014

Richard Artz · National Oceanic and Atmospheric Administration

Concerning the comment by Dr. Phillip: There are decades of measurements comparing field pH to laboratory pH measurements. Only rarely does the delta between field and lab exceed ~ 0.5 pH unit, and typically that is for samples that are near neutral. Typically differences are a couple of tenths of a unit or less and can be attributed to the loss of organic acids due to biological activity in the sample. This issue was discussed by William Keene and James Galloway in the 1980s after examining samples in remote locations such as Bermuda and Amsterdam Island. These differences are also regularly observed in AIRMoN daily samples collected by the US National Atmospheric Deposition Network. 

The sampling methodology for the samples collected by Dr. Lin was not discussed. If a funnel and bottle arrangement was used that left the funnel uncovered for an extended period of time in a dusty area, a high pH sample may well be due to contamination from dry deposition to the funnel. If a wet-only sampler of some sort was used, or if the funnel-bottle system was deployed just prior to the onset of precipitation, the value is probably correct -- and the whole source-receptor issue becomes much more interesting. If this is indeed the case, Dr. Phillip's suggestion for running a trajectory analysis is a good one. This can be handled online via the HYSPLIT model, found at:http://www.arl.noaa.gov/HYSPLIT_info.php

 Mar 27, 2014

Bommanna G. Loganathan · Murray State University

pH range you are getting is not abnormal. Acidic pH of rainwater is due to dissolution of CO2 and formation of H2CO3. Dissolution of CO2 depends on partial pressure (Henry's Law) and temperature. Check your measurement conditions (especially temperature) during the periods of relatively high and low pH. Slightly elevated pH in the initial period of rain water may also contributed by dissolution of NH3 in the rainwater. Because one of the primary species emitted to the atmosphere is NH3 produced during organic matter decomposition and emitted when the partial pressure in the soil , water, or plant is greater than the partial pressure in the atmosphere.

 Apr 1, 2014

Agron Veliu · NewCo Ferronikeli Complex L.L.C

The pH in your case in the rainwater after a time period without rain is normal because rainwater acidity depending from a lot of factors and substances that are present into the air.

 Apr 4, 2014

Harkirat S Dhindsa · University of Western Sydney

Hi Chin
It appears that rain removes acidic oxides from air that are added due to human or natural activity in the atmosphere. There are two possibilities (1) temp difference, an increase in temp of rain water can lead to do so and/or (2) the acidic oxides enter the stored rain water through the container. My experience with mercury vapours is that they can easily get into closed plastic containers to change mercury concentrations.

 Apr 9, 2014

Golam Kibria · RMIT University

The initial pH of rainwater is high, perhaps due to atmospheric load with dust particles containing CaCO3 (alkaline). The load of these dust particles apparently decreased as rain progressed and when there was not sufficient CaCO3 in the atmosphere to neutralize the acidity in the rain, the pH values progressively dropped. In general, unpolluted rain water is acidic (pH ~5.6)

Please see a paper which found a change of pH with time during one rain event, (see Figure 3) 
S. G. Tuncel and S. Ungor. 1995. Rain water chemistry in Ankara, Turkey. Atmospheric Environment 30 (15): 2721-2727.

 Apr 9, 2014

Søren Jessen · University of Copenhagen

You could calculate pH from the alkalinity assuming equilibrium with the partial pressure of CO2 in atmospheric air, and then compare that number to your measured pH.

At pH 6.5 you should be able detect quite a significant amount of alkalinity with a Gran titration. You'll typically need just 1 or a few mL sample for that, but more makes the analysis easier, of couse.

The calculation could be done in PHREEQC or any other speciation code.

 Apr 24, 2014

Richard Artz · National Oceanic and Atmospheric Administration

Keene and Galloway (Atmospheric Environment, Volume 19, issue 1 pages 199-202 in 1987 published an article called "Gran's titrations: Inherent errors in measuring the acidity of precipitation". The abstract states: "Gran's titrations are commonly used to differentiate strong and weak acidity in precipitation. However, in the course of such titrations, dissociation of the weak organic acids found in precipitation causes overestimates of both strong and free acidity. In addition, the reaction of NH4+ with OH− in the alkaline range of titrations causes overestimates of total acidity. Because of these effects, Gran's technique and related modifications have limited usefulness in characterizing the acidity of precipitation." This paper was one of the products of the Global Precipitation Chemistry Project that examined precipitation at a number of remote locations around the world. Bottom line: Be very careful using Gran's titrations for this application.

 I'm on unstable ground here. There were several responses in the literature ~ 25 years ago on the whole issue which did not result in a tidy conclusion concerning the use of Gran's titrations for precipitation samples. A strong acid is typically used to titrate well past the equivalence point. Since weak acids are often in significant concentrations in the sample solution above pH 5 or so,can it be assumed that the sample matrix is not inappropriately affected? Is there a good literature citation on the issue?

 Apr 24, 2014

Søren Jessen · University of Copenhagen

Must say I am basing this on experience right now. 

Fe-OH, Al-OH, and many other OH-complexes can be dealt with in the speciation calculation, because the computer can take their contribution to the entered alkalinity into account.

Organic acids are less easy to deal with. I've sampled peat and and humic soils though, and sometime I see a curved Gran titration-curve shape, which I attribute to organic acids with a suite of different H+ sites (different pKa-sites) becoming protonized. But mostly, I do not see that, even in water with several mmoles of DOC, meaning that bicarbonate and carbonate is much much more abundant, and/or the DOC is either not protonized or was so already before the titration began.

 Apr 24, 2014

Qiufang He · Southwest University in Chongqing

pH of rainwater always effect by the air pollutions just like many people commened. Where you collected your rainwater samples, find out the possible environment reasons. Rainwater maight influrence by the waste air from industral factory, mote from mine feild or just haze.
I suggest you analyze the anions and cations in water sample to check your data and find out the reason. pH 6.5 maight concern CaCO3 or NH3, pH too acidic miaght concern nitrate or sulfate, which both need more analysis and data to comfirm.

 Apr 25, 2014

““Praying for rain and that kind of medicine can work no matter who does it, if they do it in a strong and proper manner”

— Sun Bear from his book ‘Black Dawn:Bright Day’