NB! It seems this console command is not compatible with CS2.
Command Profile

SV_DROWNING_DAMAGE_INITIAL

CS:GO

This console command sets the initial damage per second you take as you drown. sv_drowning_damage_max is used to set the max damage this can scale to as you stay in water longer.

Syntax
sv_drowning_damage_initial [DPS]

Description

This console command sets the initial damage per second you take as you drown. sv_drowning_damage_max is used to set the max damage this can scale to as you stay in water longer.

Syntax And Arguments

sv_drowning_damage_initial [DPS]
DPS The damage per second drowning does to you. The default value for this command is 2. Set it higher to take more damage from drowning, and lower to take less damage.