A water heater replacement needs a permit in Reno, Sparks and unincorporated Washoe County. Other plumbing work depends on what is changing and which building department handles the property.
Before agreeing that a job is “too small to need one,” describe the actual work to the department. Repairing a leak and cutting out concealed piping aren't necessarily treated the same way.
A Reno mailing address doesn't necessarily put your property inside Reno city limits. Washoe County explains how to check the parcel using the Regional Mapping System and the Reno and Sparks boundary layers.
Once you know the jurisdiction, use that department's requirements. Don't use an answer about a house across town as approval for yours.
Reno: The city publishes permit information and an EZ permit process for qualifying work, including water heater replacements. Use its current guidance to check the job you're planning.
Sparks: The city lists water heaters, furnaces and relocated or added plumbing as work requiring permits. Its exemptions include specified fixture replacements and leak or stoppage repairs that don't alter existing plumbing. For an emergency repair performed without a permit outside office hours, Sparks says to apply the next business day.
Unincorporated Washoe County: The county lists exemptions for specified leak repairs, stoppage clearing and fixture work where water, waste and vent piping isn't modified or rearranged. Its guidance distinguishes those repairs from replacing concealed defective piping with new material, which requires a permit.
These are summaries. Give the department the address and description, including any piping being moved or replaced, to confirm how its rules apply.
The Nevada State Contractors Board says contractors must obtain required permits before starting work. Ask for the permit arrangements before the scheduled start, including the fee and inspection. Sparks' published after hours emergency process is a specific exception to check when relevant.
An owner doing their own work follows a separate owner builder process. If that's your plan, ask the building department about the requirements before starting.
Get the permit number and ask how to check the inspection result. A permit application and a completed inspection are different stages.
Keep the record with the job paperwork. Nevada's seller disclosure form asks about work performed without required permits, so this can come up again when the property is sold.