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 moved to the Orthodox Union (OU), later being referred to as one of their "leading experts", and ultimately held that position for over 28 years. In 2004, Belsky determined that water potentially containing tiny nonkosher organisms was kosher even if it wasn't filtered.