Water

Water, H₂O, is one oxygen atom bonded to two hydrogen atoms in a bent shape. The bend makes the molecule slightly negative on the oxygen side and slightly positive on the hydrogen side, so water molecules cling to each other and to many other substances. That's why water dissolves so much, and stays liquid over such a useful range.

Water forms whenever hydrogen burns in oxygen, but no one makes it that way for industry. Factories take it from rivers, lakes or wells and clean it. Electronics plants go much further, making ultrapure water with filters, reverse-osmosis membranes, ion-exchange resins and UV light, until almost nothing but H₂O is left. It's so pure it barely conducts electricity. A large display or chip factory can use millions of liters a day, much of it for rinsing.

In this build, water is a reactant as well as a rinse. It opens ethylene oxide into ethylene glycol, one of the building blocks of PET (polyester) film. It also turns dimethyldichlorosilane into silicone, swapping its chlorines for -OH groups that then link up into chains.