The importance of PH in Water Purification & Treatment
Most of us have such a sketchy understanding of what ph is that we simply assume that low ph water is acidic therefore corrosive and bad, while high ph water is alkaline, not corrosive and healthy. Unfortunately, like most assumptions it is wrong in so many aspects. They say “what you dont know cant hurt you”…nothing could be further from the truth with ph in water treatment
Let me try to explain in simple terms but we are going to have to delve into a little technical stuff, so please bear with me.
PH is actually a measure of hydrogen ions in a liquid. The pH logarithmic scale usually ranges from 0 to 14. Aqueous solutions at 25°C with a pH less than 7 are acidic, while those with a pH greater than 7 are alkaline. The measurement DOES NOT mean the water is inert or aggressive.
Changes from 1 point to the next are not just a single step, but a 1000 x times stronger or weaker. So a change from pH6 to pH7 is a 1000 times more alkali. That has massive impact on the water quality specifically for infrastructure and less so for health.
While a healthy pH range for Blue Drop rate drinking water is between pH 5 to 9.7, the impact of that range of pH on metal infrastructure can be devastating. The water purification authorities are less worried about this as it does not have direct impact on human health, as we consume such small quantities of water internally.
The human body has the ability to self regulate and adjust low or high ph that it consumes . By itself pH is not a big issue …but combined with other chemical content it can be terrible.
The focus on this article is the effect on infrastructure and ph’s role in damaging geyser elements, metal pipe fittings, kettle and dishwashers etc in unstable water. The actual effects and solutions are explained in depth in the sections , hardwater:limescale and soft water
Here is a pipe from a commercial building in Johannesburg business district in late 2019 which was being supplied high quality Blue Drop water with a stable pH level of 7.8
In trying to treat aggressive soft water, which is usually low ph water WITH a deficit of Magnesium and Calcium the water treatment industry would normally prescribe adding “hardness” or calcium carbonate or Soda Ash to push the pH up. In the case of very hard water with an excess of carbonates the practice is to soften the water and remove Magnesium and Calcium while keeping the pH stable at 7. It doesn’t always work.
In practical terms as you add the “hardner” media to the water and increase the pH close to the range of pH8, the water can become slimy and start to taste brackish……but there is another huge potential hidden problem, an aspect of water that very few people are aware of …..and that is the combination of chemicals, alkalinity and ph ……which can force the hardness out of the water and allow it to “precipitate”.
With the right combination of chemical and gas (carbon dioxide) in the water the water could still remain corrosive at much higher pH ranges.
This means that the water becomes so saturated with calcium and magnesium that it becomes “heavy” and the calcium sediment sinks to the bottom of whatever it is flowing through or contained in….pipes, filters, media vessels, geysers, kettles etc and can block these completely making them ineffective . Not only can it solidify on heating elements but will increase the electrical consumption leading to a breakdown of the element as each 1 mm thickness covering on the element will consume 15% more electrical power to heat it.
So if we had soft water corroding the elements, in an attempt to harden the water we now face the other extreme….it becomes alkali..yes…its not aggressive…. BUT it still damages.
Now other chemical treatments have to be added which further complicate the problem.
Some chemical and pH combinations do not cause precipitation and you can dose the water with hardening media all the way to pH10 and the water will still be partly corrosive.
A certain amount of Calcium & Magnesium is good for pipework and protects the metal surfaces from corrosion .
Water purification and treatment specialists use a mathematical formula to
determine this precipitative or corrosive quality and that water treatment calculation model is called the Langelier Saturation Index .
The bad news is that in order to correctly advise on the water treatment or water purification that a person may need it is imperative to have a water analysis done at a reputable laboratory..that is going to cost around R2 200 ex vat
Water purification or treatment can be very complicated. If it were easy we would not be facing the problems our country faces today.
If you have had a water analysis done on your borehole and need free advice then please contact us. We have the necessary experience and practical knowledge to assist.