The back flow device is located in the ground behind your water meter. The purpose of the back flow device is to act as a one-way valve in order to keep the water that has entered your water lines from returning to the City’s lines, which helps protect the water supply as a whole. A diagram of the back flow device is shown below. It is Oregon Law that once back flow devices are installed, they must be checked annually. The City contracts device testing all at once in order to save citizens some money. This $20 fee is billed each year in October on your utility bill.