Unfortunately, there's no way (yet) to treat that specific condition. One simply has to give it time to heal, and stay hydrated/warm/etc in the meantime. It goes away when the injury that caused it heals (e.g. a severe torso wound).
The good news is that it won't escalate if left unattended. As long as you can cope with the loss of water, it'll leave you otherwise unharmed. (The only other side effect is that it slightly reduces the rate that your blood supply restores.)
Two things to note:
1 - Things that increase healing rates, like resting/sleeping, hanging out in campsites, and the nanorobotic medkit, also increase the rate at which this condition goes away.
2 - This condition stacks, meaning multiple wounds that cause internal bleeding will multiply the effects.
Hopefully, some day I can add more cool stuff for medics to do with wounds. For now, they simply have a slightly higher healing rate, which is meant to simulate their knowledge of caring for wounds, avoiding infection, and protecting the wounds from re-injury.