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I recently concluded an experiment in which I followed the first method from this website -- https://www.wikihow.com/Measure-Surface-Tension . The value that I was getting is about 0.25 N/m approximately which is much higher than the actual one of .07 N/m . The water that I have been testing is Indian tap water so I assume that 1 reason why it varies so much is because of the impurities present in it. However, can anyone help me to correct the error that I am having or explain to me why the value that I am getting is actually fine?

Also, a similar experiment done by someone else https://prezi.com/1pop46g01pvr/measuring-the-surface-tension-of-water/ yielded more or less equally differing results.

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    $\begingroup$ Impurities lower surface tension not increase it. A high value has to indicate a problem with the experimental technique. $\endgroup$
    – John Rennie
    Commented Jul 31, 2018 at 4:31

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Aqueous salt solutions have a surface tension which is higher than that of pure water (surface tensions of aqueous solutions.) but your experimental result is too large to be explained by this effect.
Other impurities eg detergents have the effect of lowering the surface tension.

The same link rules out the effect of temperature on the surface tension.

Your experimental result being too large might be explained by the fact that the pivot of your apparatus “sticks” due to static friction thus giving larger readings for the force required to remove the needle from the water.

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