{"id":65824,"date":"2026-07-27T16:25:48","date_gmt":"2026-07-27T07:25:48","guid":{"rendered":"https:\/\/phys-edu.net\/wp\/?p=65824"},"modified":"2026-07-27T16:28:49","modified_gmt":"2026-07-27T07:28:49","slug":"tap-water-isnt-actually-neutral-what-a-simple-btb-test-revealed-about-the-water-you-drink","status":"publish","type":"post","link":"https:\/\/phys-edu.net\/wp\/?p=65824&lang=en","title":{"rendered":"Is Your Tap Water Secretly Alkaline? A BTB Experiment That Will Surprise You"},"content":{"rendered":"

I’m Ken Kuwako, the Science Trainer. Every day is an experiment.<\/strong><\/span><\/p>\n

“What color does BTB solution turn when you add it to tap water?”<\/p>\n

Many people would probably guess, “It’s drinking water, so it must be neutral… which means green, right?”<\/p>\n

Surprisingly, the real answer is quite different. Take a look.<\/p>\n

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Wait… Tap Water Isn’t Neutral?<\/h3>\n

It’s blue!<\/p>\n

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The BTB solution turns blue<\/b>. This result comes from testing tap water in Chiba Prefecture.<\/p>\n

If you’re thinking, “Shouldn’t tap water be neutral?” there’s an interesting piece of chemistry behind the answer.<\/p>\n

Tap water is generally close to neutral, but it is often slightly alkaline rather than exactly pH 7<\/b>. There are two main reasons for this.<\/p>\n

First, tap water is disinfected with chlorine-based chemicals (mainly sodium hypochlorite)<\/b>, which tend to make the water slightly more alkaline.<\/p>\n

Second, drinking water regulations allow the pH to range from 5.8 to 8.6<\/b>, meaning it doesn’t have to be exactly neutral. Since BTB solution appears green around pH 6.0\u20137.6<\/b>, water that’s only a little above pH 7 can already start looking bluish.<\/p>\n

From the Tokyo Metropolitan Government Bureau of Waterworks:<\/p>\n

\nQuestion: What does the pH of tap water mean?<\/p>\n

Answer: pH indicates how acidic or alkaline water is. The scale runs from 0 to 14, with pH 7 being neutral. Lower values are more acidic, while higher values are more alkaline.<\/p>\n

Japan’s drinking water standard requires tap water to remain between pH 5.8 and 8.6 to help prevent corrosion in water supply facilities. Tokyo’s tap water typically has a pH of around 7.5, making it close to neutral.<\/p>\n

https:\/\/www.waterworks.metro.tokyo.lg.jp\/faq\/qa-22.html<\/a>\n<\/p><\/blockquote>\n

From the Chiba Prefectural Government:<\/p>\n

\nBecause lead is less likely to dissolve in alkaline water, Chiba Prefecture has adjusted tap water to be slightly alkaline throughout its water supply system since April 2002.<\/p>\n

https:\/\/www.pref.chiba.lg.jp\/suidou\/kyuusui\/namari\/03qa.html<\/a>\n<\/p><\/blockquote>\n

I also tested the water in my laboratory, and it turned blue as well.<\/p>\n

That said, tap water isn’t guaranteed to be alkaline everywhere in Japan.<\/b><\/p>\n

Although sodium hypochlorite used for disinfection tends to raise the pH, the final value also depends on the original water source\u2014such as rivers, reservoirs, groundwater\u2014as well as local geology and dissolved minerals.<\/p>\n

As a result, some regions have water that’s almost perfectly neutral, while others may even be very slightly acidic. So it’s more accurate to say that disinfection generally pushes tap water toward the alkaline side.<\/p>\n

Blow Into It… and Watch the Color Change!<\/h3>\n

Now for the fun part.<\/p>\n

Take the blue tap water and slowly blow into it through a straw. As you do, the color gradually changes from blue \u2192 green \u2192 yellow<\/b>.<\/p>\n

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Watch the experiment here.<\/p>\n