In 1987, he transferred to the Orthodox Union (OU), eventually being described as one of their "chief experts", and ultimately served in that capacity for more than 28 years. In 2004, Belsky ruled that water that might contain microscopic nonkosher organisms is kosher even if it is unfiltered.
In 1987, he transferred to the Orthodox Union (OU), becoming known as one of their "principal experts" and serving in this role for over 28 years. In 2004, Belsky ruled that water containing microscopic nonkosher organisms was still kosher, even if it wasn't filtered.