It is known that three people drink three glasses of water three days and three people drink nine glasses of water nine days.

Then nine people drank 27 glasses of water for nine consecutive days.

2、

It is known that three people drink three glasses of water for three days and one person drinks one glass of water for three days.

Then one person drinks three glasses of water for nine days, and nine people drink twenty-seven glasses of water for nine days.

3、

1 person needs 1 bucket of water for 3 days, so it is concluded that 1 person 1 day needs 1/3 bucket of water.

9 people for 9 days, the formula is: 1/3×9×9 = 27.

So the answer is 27 barrels of water.

4、

Three people drink three buckets of water for three days, which is similar to () one person drinks () buckets of water for one day and two people drink two buckets of water for two days. ...

According to this format, nine people and nine days are naturally nine buckets of water.

Such a brain teaser cannot be explained by mathematics.