noun
water repellency
Refers to the property of a surface that repels water, often used in contexts like fabrics, coatings, and outdoor gear.
このジャケットは撥水加工が施されている。
This jacket has a water-repellent treatment.
撥水スプレーを靴に吹きかける。
I spray water-repellent spray on my shoes.
防水 means 'waterproof' (completely impervious to water), while 撥水 means 'water-repellent' (water beads up and rolls off but may eventually soak through under pressure).
Compound of 撥 (repel, brush aside) and 水 (water). The reading はっすい is a regular on'yomi combination with gemination.