Water and milk are uncountable.
I say -
This bucket has the clean water, that bucket has the dirty water.
The white jar has milk in it; the blue jar has water in it.
If you mean a specific set of data, then use "the", if you mean data in general, then "the" is not used.
This file has the model data from the last simulation run.
Files with the extension ".mod" have model data; files with the extension ".vid" have video data.