I wonder if "Hydrogen (rich) water" is known to people in overseas.

Hydrogen water in aluminium cansAluminum cans of hydrogen water were distributed to foreign press at the G20 conference in Japan last year.

singular noun goes with "was", while plural noun goes with "were"

It appears that the Ministry of Foreign Affairs meant to show off how Japan deal withis building a sustainable society so that they didn't serve withby not serving plastic bottles.

By the way, some people seriously believes that Hydrogen water is good for their health because hydrogen molecules remove reactive oxygen species infrom their body.

I guess "reactive oxygen species" is a technical term so okay as is

Though I totally disagree with the above statement, it isn't easi's harder than I thought to verify that it is false from a scientific perspective.

Avoid the double negative to make it easier on the reader

Some articles saidy that hydrogen molecules depressedreduce blood pressure, inflammation, and fatigue by removing reactive oxygen species.

It is hard to deny the efficienacy of hydrogen molecules itself without ascertaining the reliability of those articles.

efficiency asks how well it works, but efficacy is asks whether it works or not

The most easiest explanation is that it is nearly impossible to retain a high enough concentration at which those effects arecan appeared.

Hydrogen water in aluminium cans wereas distributed to the foreign press at a G20 conference in Japan last year.

It appears that the Ministry of Foreign Affairs meant to show off how Japan deal withis building a sustainable society so; that's why they didn't serve withe Hydrogen water in plastic bottles.

(or "I wish they quit making a fool of themselves. ")

Both make sense!

By the way, some people seriously believes that Hydrogen water is good for their health because hydrogen molecules remove reactive oxygen species infrom their body.

Though I totally disagree with the above statement, it isn't easi, it's harder than I thought to verify that it is false from a scientific perspective.

"it's harder than I thought" is a commonly used phrase

I also removed "statement" to clarify that you're disagreeing with the claim that "hydrogen water is good for their health because hydrogen molecules remove reactive oxygen species from their body", and not the entire statement that "some people seriously believe that Hydrogen water is good for their health because hydrogen molecules remove reactive oxygen species from their body."

Some articles saidy that hydrogen molecules depcresased blood pressure, inflammation, and fatigue by removing reactive oxygen species.

It is hard to deny the efficiency of hydrogen molecules itself without reliability of those articles.

This sentence doesn't make sense, but I'm not sure how to correct it because I can't understand Japanese yet.

The most easiest explanation is that it is nearly impossible to retain the high concentration at which those effects are appeared.

I wonder if "Hydrogen (-rich) water" is known to people in overseas.

Hydrogen water in aluminium cans wereas distributed to the foreign press at the G20 conference in Japan last year.

hydrogen water was distributed -- the water is the subject of the sentence, not the cans, so you need a verb that goes with a singular noun.

It appears that the Ministry of Foreign Affairs mewanted to show off how Japan deal withis building a sustainable society, so that they didn't userve with plastic bottles.

By the way, sSome people seriously believes that Hydrogen water is good for their health because hydrogen molecules remove reactive oxygen species infrom their body.

Though I totally disagree with the above statement, it isn't easi harder than I thought to verify that it is false from a scientific perspectivexpected to prove scientifically that it is false.

Some articles saidy that hydrogen molecules depressedreduce blood pressure, inflammation, and fatigue by removing reactive oxygen species.

I'm not sure what you mean by 'oxygen species'. Species is definitely not the right word -- usually it refers to types of plants or animals.

It is hard to deny the efficiency of hydrogen molecules itself without reliability of those articles.

I don't know what you are trying to say.
The articles are not reliable, so maybe the hydrogen is not as effective as they say.??
Or:
I can't disprove that hydrogen has these effects because there are no articles explaining why it can't work.??

The most easiest explanationlikely reason (why hydrogen doesn't work?) is that it is nearly impossible to retainmaintain the high concentration at which required for thoese effects are appeared.

I wonder if "Hydrogen (rich) water" is known to people in overseas.

Hydrogen water in aluminium cans wereas distributed to foreign press at the G20 conference in Japan last year.

It appears that the Ministry of Foreign Affairs meant to show off how Japan deal withis building a sustainable society so that, they didn't serve withater in plastic bottles.

(or "I wish they would quit making a fools of themselves. ")

By the way, some people seriously believes that Hydrogen water is good for their health because hydrogen molecules remove reactive oxygen species in their body.

Though I totally disagree with the above statement, it isn't easi's harder than I thought to verify that it is false from a scientific perspective.

Some articles said that hydrogen molecules depressed blood pressure, inflammation, and fatigue by removing reactive oxygen specimolecules.

It is hard to deny the efficiencyacy(?) of hydrogen molecules itself withoutthemselves without knowing the reliability of those articles.

The most easiestlikely explanation is that it is nearly impossible to retain high concentrations at which those effects are appeared.