There are no specific rules for drowning in DnD 5e; however, there are rules for suffocating, which can be used for drowning. A creature can hold its breath for (1 + Constitution modifier) minutes (minimum 30 seconds).

When a creature runs out of breath, it survives (Constitution modifier) rounds (minimum 1). At the start of its next turn, it drops to 0 hit points and starts dying (making death saving throws).

For example, a creature with 16 Constitution (+3 modifier) can hold its breath for 4 minutes. After that, it survives for 3 rounds (18 seconds). On the 4th round, it falls to 0 hit points and is dying.

Matt Zane

Author, DnD Lounge

Matt Zane started DnD Lounge in 2021. Matt began playing DnD 5e in 2015, and has been DMing since 2017. He loves optimization, but also enjoys looking for creative ways to use spells and abilities that follow the spirit and letter of the rules. He also eschews pure optimization in favor of a more balanced approach, where building a character is primarily about serving an interesting story arc and party dynamics rather than maxing out DPR.