
Chilled water is plain still water, served cold — used to dilute a drink, not to flavour it.
No flavour or aroma — clean and neutral.
Cold water cools and dilutes a drink with a known amount of water, more precisely than melting ice. A splash also softens a strong spirit and opens up its aroma.
Any neutral still liquid can add the same small dilution. Just don't use sparkling water — the bubbles would change the drink.
Cold water is still; soda water is carbonated, with bubbles and a light prickly tang. Both are near-neutral and clear and both dilute a drink, but only soda has bubbles.
Unlike soda water, it has no carbon dioxide, so no bubbles.

Sazerac
Rye whiskey, Bourbon, Brandy

Old Fashioned – IBA
Bourbon

Absinthe
Absinthe

Caipirinha (low-calorie)
Cachaça

Derby
London dry gin

Mint Julep – IBA
Bourbon

Absinthe Frappé
Absinthe

Limeade
Non alcoholic

Rum Punch
White rum

Bruised Pomegranate
Rye whiskey, Byrrh

Cardamom Daiquiri
White rum

Gin Punch
London dry gin

Gold Cocktail
Blended Scotch whisky

Golden Retriever
Light gold rum

Planter’s Punch
Jamaican aged rum

Turf Club (1939 recipe)
Old Tom gin, London dry gin

Mexican Nail
Tequila reposado

Mizuwari
Blended Scotch whisky

Canchánchara – IBA
Aguardiente