Candlewick

The primordis swamp is known for it's deadly & hostile environment. One of the greatest examples of that are candlewick parasites. Inhabiting the waters of the swamplands, candlewicks are extremely heat resistant, allowing them to survive boiling temperatures. Because of this, improper filtration before attempting to purify the water isn't likely to remove candlewicks. 
When candlewicks get into your system they take route within the intestinal tract, feeding off the nutrients as they pass through at first, but over time as they become more embedded within the intestine, taking more & more nutrients from the host, it begins to trigger an additional reaction which causes the body to heat up over time. This in conjunction with the slowly withering form as less & less nutrients are absorbed into the body leads to the effect that gave the parasite its name; like a lit candle, the wax around the wick melts away to fuel the slowly burning fire.
There are fortunately a number of oral medications which can treat an infestation of candlewicks, which are incredibly effective thanks to them residing in the intestines. In an emergency, they can be semi-effectively starved out by going a week or two without food, only subsisting on water. This can cause intestinal damage depending on how many candlewicks are present in the intestine & how long they've been there, with stomach cramps & vomiting common side effects of the treatment as the candlewicks try to pressure the body into providing more sustenance. Eventually, the candlewicks will either die from starvation or leave your system alongside the water you're subsiding on.
Candlewicks are susceptible to cold temperatures, a fact that means some creatures with lower natural body temperatures have some natural resistance. Freezing the water for 5 minutes is enough time to kill any off entirely, though is unlikely to be achievable without an elemancer present; any other person prepared enough to clean the water that thoroughly would be better off bringing more clean water.

Type

Parasitic