What is pH of Water and how relevant it is for Urban Water Quality?
Do you know from your washbasin turning green to your gastrointestinal problem are all related to the pH of water you drink? Check out this guide to know all you need about pH of water.
What do you mean by the pH of water ?
pH of water for water quality sounds kind of strange right? Actually the taste of water you drink owes it all to its pH. It is in fact such an important attribute to water quality that it even determines how the water we intake reacts, when it comes in contact with a variety of body fluids of different pH.
To make it more clear if you can recall, you must have come across acids and bases at your school. Remember. Yes! Those acids and bases differ from one another in their pH level.
The extent of a liquid being acidic or basic in nature depends on its ion composition. This composition is represented in pH. pH is a measure of the relative amount of free Hydrogen and Hydroxyl ions present in it. As we know water when breaks down results into:
[ H2O ] = [ H+] + [ OH-] to release Hydrogen and Hydroxyl Ions respectively.
The representation of this ion composition on a scale is known to us as a pH Scale.
⦁ pH Scale
The pH of any liquid is represented in logarithmic units.
pH = -log[H+]
These values when represented on a scale has a range from 0 to 14. To understand the logarithmic meaning of pH of a solution:
It means a solution with pH 1 will be 10 times more acidic than a solution with pH 2.
The pH scale range between 0 to 14 such that
At 25 °C, A solution having reading on a pH scale of:
⦁0 --> Highly Acidic
⦁7 --> Neutral
⦁14 --> Highly Basic
⦁ pH Balance
As we have discussed amount of free Hydrogen and Hydroxyl ions present in a solution determines its pH. If the number of Hydrogen ions equals that of Hydroxyl ions then the solution can be said to be a completely pH balanced solution.
For water pH balance, if water solution at 25°C has,
No of positive Hydrogen ions = No of negative Hydroxyl ion = 7 or,
pH = pOH = 7 so that
pH + pOH = 14
then we can state that it is a completely pH balanced water solution.
⦁ Acids and Bases
If a sample liquid at 25°C has
pH < 7
Then number of Hydrogen ions[ H+] > number of Hydroxyl ions[ OH-]
This indicates that the above solution is Acidic in nature.
If a sample liquid at 25 °C has pH > 7
Then number of Hydrogen ions[ H+] < number of Hydroxyl ions[ OH-]
This indicates that the above solution is Basic in nature.
⦁ Alkalinity and alkalis
Alkalinity is the measure of the capacity of a liquid to resist any change in its pH. It is the amount of acid that a liquid can neutralize in order to resist any change in its pH. It is hence a measure of the tendency of a liquid to maintain a fairly balanced and stable pH level.
Alkalis are bases that are soluble in water. Not all bases are soluble in water. This is why the famous term goes:
"All alkalis are bases but all bases are not alkalis"
Example of an alkaline : Sodium Hydroxide [NaOH].
Why analyze pH for Water Quality?
The pH of any liquid explains how reactive or non reactive the liquid is. It determines how reactive water will be when it comes in contact with different organic and inorganic elements in nature.
Water solubility determines how sustaining the water will be for the aquatic and wildlife depending on various dissolved minerals in water. For Eg. from the availability of crucial nutrients like nitrogen and phosphorus to how much the aquatic life can use them effectively to survive all depends on the pH of water. Any change in pH can have a devastating effect on its inhabitants and so the environment.
Every liquid has its pH. The human blood for instance also maintain a certain pH level at which body works best. Water pH if too high or low can cause severe implications in metabolism and body functions.
Over the years as we have started acknowledging the importance of pH in our drinking water, more and more research have brought to us the benefits of alkaline water that really make a difference when it comes to body metabolism.
pH is so critical a factor in oil and biodiesel production plants that it is used to control the microbial growth rate. This is because the activity of enzymes are dependent on the concentration of Hydrogen ions [pH] in the solution.
Water during the course of its flow in river or stream may dissolve certain minerals like calcium. This could change its pH making it more alkaline in nature.
The air pollutants like Nitrogen Dioxide and Sulfur Dioxide released from burning coals and emissions from vehicles and factories remain suspended in air. These air pollutants dissolves in the rain drops and form acid. This acidic water through leaching and as runoffs fall into the rivers and lakes. This increases the acidity of water.
Urban Water pH Standards
Alkaline water can be used for drinking but acidic water should be generally avoided.
Since pH is an aesthetic quality of water there is no tight regulation regarding the same.
But there are certain recommendations regarding the pH of drinking water.
United States Environmental Protection Agency recommends:
Drinking water pH : Should lie between 6.5 - 8.5 on a scale ranging from 0 to 14.
Operations: Detect, Measure, Test & Treatment
A change in pH cannot be detected visually. Instead a pH paper is used to identify the change. The pH paper is coated generally with a chemical named Flavin with changes color on being exposed to solutions of different pH.
Working of a pH paper:
⦁ Hold the paper from one end and dip the other end of the paper into the sample to be tested.
⦁ A color change is observed on the pH paper.
⦁ Using a pH scale match the color of the pH paper to the scale.
⦁ The the correct pH of the sample is thus obtained.
Many pH test stripes are available in the market that gives accurate results.
The change in water pH has nothing to do with odor. If at all there is any specific odor, it could be that of the impurity dissolved in it responsible for the change in its pH.
Many built-in pH meter are available in the market.
Mostly the municipal water supplies are regulated and maintained around pH 7. But if you happen to observe rustiness or whitish, blue color change of your faucets or pipeline you should check the pH and hardness of water.
Home testing kits are available in the market.
Urban Water pH Treatment
Using pH adjusting salt to alter the pH level of water.
If you observe the pH of water to be highly acidic and you will want to alter it. It can be easily done through pH adjusting salts available in market.
It is a fairly easy and inexpensive way to alter the pH.
The more acidic the water is, lower is the biodiversity it supports. High acidic water are highly corrosive in nature, dissolving and destroying everything in its path of flow.
Low pH water are highly corrosive acids. They can dissolve heavy metals and cause damage to the supply pipelines, bridges and other metal constructions.
High pH water are bitter in taste and can be a nuisance when it comes to washing and cleaning.
Water in abandoned coal mine has a lot of minerals dissolved in it. This makes its pH fall to a level as low as 2. A liquid of a pH 2 could be highly corrosive and unsustainable to life.
Due to excessive emissions a new problem is facing the humans in the form of Ocean Acidification.
Alkaline water through recent studies has proved to be good to human health upon consumption.