Poison and Water

I am composed up of a nasty mixture of poison and water.
The sip you take to quench yourself will be the same sip used to slaughter.
It drains out from every pore on my skin.
It floods from my eyes, my mouth and my grin.
The combination of the two has covered me in a rash with a silent itch.
Once I lost my footing my mind followed and it's been that way since.
I cannot control when it is one or the other,
or when it's both of the two working together.
The combination of the two has covered me in a rash only I can see.
But I am unaware of how long it will take to finally kill me.