A soil meter cannot be used with water because accuracy and consistency are fundamental traits that a meter must provide.
Why Can’t You Use a Soil pH Meter for Water?
The testing range offered by soil pH meters is often very limited for the needs of a water system. A sample of water relatively low in pH will measure towards the top on a soil meter — assuming the meter will measure it. Soil meters will likely produce inaccurate and inconsistent results because they are not designed with water in mind.
A soil meter will always give you an answer for the pH of whatever is being tested, but these are random numbers as far as we’re concerned. If you are bothering to find out the pH in the first place, you need an accurate number. Plants can only tolerate a certain pH balance, and we need to know what’s going on to keep them healthy and thriving.
For all of the reasons we mentioned above, you just won’t get an accurate reading if you measure the pH of water with a soil meter.
Measuring the pH of water with a soil meter is like checking a broken clock and hoping it happens to right. If you’re just checking to check, use a soil pH meter to your heart’s content. When the pH affects the existence of living, growing things: get a meter that was made for what you’re using it for. You will quickly realize that a meter you can’t trust isn’t really a meter at all.