Only rainwater harvesting systems that use a pump to use the rainwater out of the cistern is required to obtain an auxiliary water permit from the City of Austin. Therefore, if you are installing a rainwater harvesting system without a pump, then you don’t have to worry about a permit.
In addition, if you are installing a pump on the system, you will be required to install a special backflow prevention device called a Reduced Pressure Zone (RPZ) backflow prevention device at your water meter.
But now you may be asking, “I won’t be connecting my pressurized rainwater harvesting system to any municipal water pipes. Why do I still need to install this RPZ backflow prevention device?”. The simple answer is that your pressurized rainwater harvesting system has the “potential” to push untreated rainwater back into the municipal water grid just due the presence of the pump if a pressurized rainwater pipe somehow becomes connected to your house’s plumbing system. The pump can produce higher pressures than the municipal water pressure at your house, therefore pushing rainwater into the municipal water grid.
If you are not in the City of Austin, you definitely want to check with your municipality as they may have different permit requirements.