Full Idea
Water is said not to be 'dissective', since there are parts of any quantity of water which are not water.
Gist of Idea
Dissective: stuff is dissective if parts of the stuff are always the stuff
Source
Peter Simons (Parts [1987], 4.2)
Book Reference
Simons,Peter: 'Parts: a Study in Ontology' [OUP 1987], p.139
A Reaction
This won't seem to do for any physical matter, but presumably parts of numbers are always numbers.
Related Ideas
Idea 17426 A concept creating a unit must isolate and unify what falls under it [Frege]
Idea 17437 Non-arbitrary division means that what falls under the concept cannot be divided into more of the same [Frege, by Koslicki]