What is the percentage of getting HIV from a used syringe found in a drain?

well i think the biggest thing is does the person who has the syringe if they have hiv or someone else who used it before it got in the drain the big part is there might be a big chance it might aquire a infection if it was in the drain i sure wouldn't use it to many times taking a chance dirty turn rusted thats why needles need to be exposed of so you don't catch anything from it so theres a big chance it is infected with something it doesn't have to be hiv