The phrase "watery fluid" refers to a liquid substance that has a consistency similar to water. It means a fluid that is thin and transparent, like water, rather than being thick or sticky. Full definition
It is unlikely that the author or any of his readers would have realised the significance of the separated watery fluid that he records coming out with the blood. (premierchristianity.com)
A green or red watery fluid is likely coolant from the cooling system. (yourmechanic.com)
According to Ziment, «they trigger a sudden release of a wave of watery fluids in the mouth, throat and lungs. (fieryfoodscentral.com)