A fluid sensor assembly for a washing machine appliance is provided herein. The fluid sensor assembly may include a first conductivity rod, a second conductivity rod, and a chamber sheath. The first conductivity rod may extend between a top rod end and a bottom rod end. The second conductivity rod may extend between a top rod end and a bottom rod end. The chamber sheath may include a non-permeable sidewall and a sealed top wall. The non-permeable sidewall may extend about the first conductivity rod from a top sheath end to a bottom sheath end. The top sheath end may be positioned on the sealed top wall. At least a portion of the bottom sheath end may be positioned above the bottom rod end of the first conductivity rod. The non-permeable sidewall may be radially spaced apart from the first conductivity rod and define a radial chamber therebetween.