While collecting rain in a barrel for your garden is generally unregulated, piping that harvested water through the walls of your house and into a toilet transitions you into the realm of municipal building codes. Plumbing codes exist to protect the public water supply from cross-contamination and to ensure residents have access to safe sanitation. Before cutting a single pipe, you must understand the rules governing non-potable indoor systems.
The ICC and IPC Guidelines
In the United States, most local municipalities base their specific plumbing laws on the International Plumbing Code (IPC), specifically Appendix M (or Chapter 13): Nonpotable Water Systems. While local variations exist, the core requirements are almost universally identical across jurisdictions.
1. Visual Identification (The Purple Pipe Rule)
Building inspectors are terrified of future homeowners accidentally hooking a drinking fountain up to an unfiltered rainwater pipe. Therefore, all pipes carrying non-potable water must be visually distinct from potable (drinking) water lines.
By international standard, non-potable pipes must be purple. If you are using PEX tubing, you must buy purple PEX. If you are using PVC or copper, the pipe must be painted purple, or continuously wrapped in purple marking tape that states "CAUTION: NONPOTABLE WATER, DO NOT DRINK" every five feet.
2. Backflow Prevention Mandates
As discussed in our previous articles, any system that connects a rainwater tank to a house that is also hooked up to the city grid must have a backflow preventer. The code strictly dictates the type of device. Usually, an RPZ (Reduced Pressure Zone) valve is the bare minimum requirement for dual-supply switch-over systems. This valve must be tested immediately upon installation by a certified professional, and often tested annually thereafter.
3. Fixture Labeling
Every point of use where rainwater is discharged must be physically labeled. If your rainwater goes to an outdoor spigot, that spigot must have a permanent metal or plastic tag that says "Non-Potable Water - Do Not Drink." If it goes to a toilet, the shutoff valve behind the toilet must be similarly labeled.
4. Roofing Material Restrictions
If you are bringing water indoors, even just for laundry, the code may dictate what type of roof you can collect from. Wood shake roofs (which harbor excessive bacteria) and roofs treated with toxic biocides (zinc or copper strips for moss control) are frequently explicitly banned as collection surfaces for indoor non-potable systems.
Permits and Inspections
Do not attempt an indoor rainwater retrofit without pulling a permit. An unpermitted, illegal cross-connection that contaminates a municipal water main can result in massive fines and criminal liability. Hire a licensed plumber who understands local chapter 13 variations, pull a permit, and proudly show the inspector your purple pipes and air gaps.