I’m in the depths of getting wool skeins dyed, and don’t have any of that ready to show to the world yet. Its a lot slower and more complicated to get from water sample to dyed wool when taking measurements at every step on the way, but it’ll be good in the end. Hopefully I can remember to stir the next batch more so they are less blotchy. <sigh> But I digress! There’s three main things I’m looking at in the water: pH, Total Dissolved Solids (TDS) and iron content (ppm). Let’s have a chat about each of those in turn and today we’re going to chat about pH. There’s a lot of complicated chemistry involved in water, and there’s quite a bit of interplay between all three (and temperature, and and and).. I mean, you can get a whole university degree in water, so know that we’re aiming for broad strokes here and big picture.
The one that most people are familiar with on any level is pH, the measure of how acidic or basic something is. It’s measured by looking at the free hydrogen ions (H+) in the solution. (Inversely proportional, as a note: More hydrogen, lower pH.) It’s a scale that runs from 0-14, with acidic things down low and basic things up high. Pure water is the control, and it sits at 7.0. A few things people don’t realize (or remember from high school chemistry) is that the scale is logarithmic, which basically means that the distance (or number of hydrogen atoms) in going from 7 to 6, is not the same as the distance from 6 to 5. There’s 10 times as many in that second chunk. That’s trivia level content more than super relevant to anyone reading, but if you ever wanted to try and count hydrogen atoms.. well we can talk about new hobbies, hmm?
When reading the WHO Guidelines on drinking water (1) , a pH anywhere from 6.5 to 8 is considered acceptable. Pure water, remember, hangs out at 7 exactly, but there’s a lot of elements that affect the pH without making the water undrinkable. All of us who lived through the pollution filled 1970s and 1980s remember the screams about acid rain and how it was melting away everything, I think. Pollution can affect the pH of water, but by the same token, most ground water has absorbed enough minerals that it slides itself a little higher on the pH scale. (And you pay extra for all those minerals at the store when you buy spring water.. s’okay, they are generally what makes water taste better. Distilled water always tastes flat and weird.)
So clearly everything below 6.5 and above 8 is dangerous, right? Well, not so fast. Where it gets more complicated is that pH alone is not an indicator of safety. Common household vinegar has a pH of approximately 2.8, which is extremely low.. in the same range as stomach acid, but we think nothing of ingesting vinegar (ideally on a nice hot plate of fries.. mmmm.) It is a weak acid, a well diluted acid, generally sitting at about 5% strength. If it was full strength, it would be very dangerous indeed!
Further complicating matters is how pH and other measures interact. pH is extremely dependant on temperature (not much of a consideration for me, all of my samples were at room temperature), and the pH of water can determine its tendency to have picked up other ions. As the pH gets lower, the metals are more soluble.. they dissolve more easily in the water, so there tends to be more lead, copper, iron etc in water that tends towards the acid. We’ll talk more about metals in water when we have a better look at the iron testing that I did and how that affects the dye works.
Water chemistry is complicated and while I knew it was a big field to go poking into, it’s been a fast train into the depths. It’ll take a lot more digging to get myself out of these weeds.
- World Health Organization – pH in Drinking water (2007)
- Safewater.org TDS and pH (2017)
- Health Canada – Guidelines for Canadian Drinking Water Quality: Guideline Technical Document (2015)