Are the Ice-Water/Boiling water thermometer calibration methods accurate?

[sealer39]

I'm sick of it, seems like I can't find an accurate thermometer, I have 3 types of thermometers, digital, alcohol and mercury, none of them have the same reading in equal conditions, I wanna try the ice water/boiling water methods but I wanna see if this is accurate because the percentage of water contamination is different in different regions and that affects freezing/boiling point

Buy some bottled water.

 

[Kiki]

@Kiki You have some experience/thoughts on this?

https://www.epicurious.com/expert-advice/how-to-calibrate-a-thermometer-step-by-step-article