Pour the water into a glass or mug. If using warm water, heat it until just comfortably warm — never boiling.
Add 1–2 teaspoons of apple cider vinegar. Start with 1 teaspoon if this is your first time.
Stir in the lemon juice, honey, and cinnamon if using, until the honey dissolves.
Taste and adjust: add more water if it's too tangy, or a touch more honey to soften it.
Drink through a straw if you like, which keeps the acid away from your teeth.
Rinse your mouth with plain water afterward and wait 30 minutes before brushing.