one safe way to approach this:
i use an infuse drip with an dedicated amount of drops per volume.
example 20 drops for 1 ml
i calculate the amount of charcoal to be used per time frame
example 1 kg / hr
i use for starters 7 to 15%, by weight, from the charcoal
in this case: 1 kg charcoal = 70 to 150 ml water drip
1 ml = 20 drops, 70 ml = 1400 drops, 150 ml = 3000 drops
1 hour time frame for 1 kg charcoal + water drops
1 hour = 3600 seconds
in this case : 1400 drops in 3600 seconds is one drop every 2,571 seconds or 23 drops per minute.
3000 drops in 3600 seconds is one drop per 1,2 second or 50 drops per minute
this is a safe staters amount, even for direct drip in, without a pre heating coil.
since i use a coil and higher temperatures in the core, the waste heat vaporised the water already in the coil, i have used water up to 50% already