Oatey® H2O No. 5 Paste Flux is a water flushable soldering paste flux designed to clean and flux most commonly soldered metals. 100% lead free, H2O No. 5 is NSF listed for potable water applications. Its formula resists turning copper piping green and is excellent for large diameter copper pipe applications. Made in the USA. Oatey products have earned the trust of plumbing professionals for over 100 years.