What is The pH of Rainwater?

What is The pH of Rainwater?

When we generally think of water, we think of something that is pure and clean.  Something that contains, well, nothing but water.  That is an ideal in many situations, but not something you’ll often encounter unless you have distilled water.

When you normally encounter water, it will have minerals and other things in it.  These things can be good or bad depending on what they are, and in some cases they can be quite normal.  For example, if you have spring water, it could be normal for it to have minerals dissolved in it.

When you think about rainwater, you might think that what falls from the sky might, in some sense, be pure.  After all, it evaporates, and condenses, and then falls, and seemingly might not encounter anything from the sky to the earth.

This isn’t actually the case though.  When rainwater falls it encounters a lot in the atmosphere and that’s one of the reasons why it differs from distilled water, water from your tap, and other types of water.

The difference we are going to look at today is pH.  You might know that the pH of water that has nothing in it besides water is 7.  This means that water is neutral.  It isn’t basic or acidic.  Rainwater has a different pH.  That’s what we’re going to look at in today’s TrueTreeTalk blog post.

What is the pH of Rainwater?

The pH of rainwater can vary geographically and depending on a variety of conditions, but generally it will have a value that’s between 5 and 5.8, with an average of around 5.6.  This means that regular, “normal” rainwater is on the somewhat acidic side.

Why is Rainwater Normally Acidic?

Rainwater is normally acidic because of carbonic acid.  Carbonic acid forms when CO2  and water combine.  There is a natural amount of carbon dioxide in the atmosphere and also an amount that is contributed by human activity.  The carbonic acid is what makes rainwater acidic.

If Rainwater is Normally Acidic, What is Acid Rain?

You may have heard the term “acid rain” before.  Since rainwater is naturally acidic, it might seem a little redundant.  Acid rain refers to rainwater that is more acidic than normal.  It’s a value that is less than what would be normal for an area.  Although you might not be as familiar with it, rainwater can also be basic.  In this case, its pH would be higher than normal.

What Causes Acid Rain?

Acid rain is caused by nitrogen oxides and sulfur dioxide that are released into the atmosphere.  They generally come from power generation from fossil fuels and automobiles with gas/diesel engines.  The pH of acid rain can be around 4.  Remember that the pH scale is logarithmic, so going from 5 to 4 indicates an increase of ten times the acidity.

Is the Natural Acidity of Rainwater Bad for Plants?

Although what is good and bad for plants can vary based on a number of criteria, the general answer to this is no.  Plants that are growing naturally should be adapted to the normal pH of the rainwater in their area and may even benefit from the slight acidity of it.

Is Acid Rain Harmful?

Rainwater that is more acidic than normal can have some harmful impacts.  Acid rain can wash away things in the environment that can neutralize the acid, it can cause nutrients in soil to dissolve, it can cause the release of aluminum into soil, it can take nutrients away from tree foliage, it can cause things such as aluminum to build up in bodies of water, and it can have an effect on man-made structures, for example by damaging paint and things made of stone.

What’s the pH of Tap Water?

This can vary a great deal depending on where you live and how your water is filtered.  If you live in an area with hard water, you might find your tap water has a pH of 8.0, which is a great deal different from the average pH of normal rainwater.

Is the pH of Rainwater the Same Everywhere?

The pH of rainwater can vary geographically.  For example, we came across a map that showed generally lower pH levels for rainwater in the east, and in particular, in the northeast of the United States.  The map was from 2002, but it does illustrate the idea.  Although this difference could be due to industrialization, the natural pH of rainwater could also vary geographically.

If you liked learning about the pH of rainwater check out our other posts on our TrueTreeTalk blog.  Follow us on Facebook to keep up with these and other posts.

*          *          *

ArborTrue is a science-based tree-service company in the greater Houston area.  We provide a range of services including tree trimming, tree pruning, tree removal, tree planting, arborist consultations, and more.  Call us today at 832-980-8733 or reach out to us online to schedule an appointment.