Why not use pure methanol or pure ethanol when extracting some components from natural products, but methanol or ethanol with a certain water content?

Anhydrous methanol or anhydrous ethanol will absorb water soon after opening a bottle. If gas chromatography is used, the water content will affect the result of precise analysis, so "Anhydrous XX" will be written. And the placement of anhydrous methanol and ethanol should be paid attention to and required.

Generally, the extraction of natural products can't avoid introducing water, so it is unnecessary to use anhydrous water, and the cost of anhydrous water is higher.

What's more, solutions with different proportions of water and methanol and ethanol are sometimes more suitable for the extraction of products, and have less volatility, which is more conducive to protecting the experimenter and measuring the volume more accurately.