Sarayu (सरयू) is the Sanskrit name for the sacred river that flows past Ayodhya — birthplace of Lord Rama. From sṛ (to flow) and vāyu (air).
Sarayu is widely used in India.
Sarayu does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Sarayu reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.