The Water Cell is a fluid cell added by TechReborn. You can get by using an empty cell on a water block.
Chemical Reactor recipe:
Compressed Air Cell + Hydrogen Cell → 2xWater Cell
Industrial Electrolyzer recipe:
32x Sugar + 7xEmpty Cell → 2xCarbon Cell + 5xWater Cell
Chemical Reactor recipes:
Nitrocarbon Cell + Water Cell → 2xGlyceryl Cell
Sulfur Cell + Water Cell → 2xSulfuric Acid Cell
Industrial Electrolyzer recipe:
Water Cell → Electrolyzed Water Cell
Solid Canning Machine recipe:
Water Cell + 2xTin Ingot → 2x10k Water Coolant Cell
Industrial Grinder uses water which could be supplied from cells to give better yield from grinding ores.
Industrial Sawmill uses water which could be supplied from cells to give better yield from milling logs.