Short answer: if your water heater is leaking in Walnut, close the cold-water valve on the heater, keep clear of electrical hazards, and call. Much of Walnut’s water comes through Walnut Valley Water District, whose 2025 report shows hard water, so scale and corrosion are common causes. Our water heater leak repair in Diamond Bar guide covers the first steps, and the plumber you speak with will confirm whether they cover your Walnut address.
What is different about water heater leaks in Walnut
Walnut Valley Water District says it serves portions of Walnut, and the district’s water quality report is the best place to see what is coming out of your tap. In its 2025 report, the district lists average hardness of 234 mg/L for the Metropolitan Water District Weymouth supply that makes up about 60 percent of its water, and 97 mg/L for the Miramar supply that makes up about 39 percent. That is roughly 14 and 6 grains per gallon by our conversion. Which blend reaches a given street depends on where you live, so it is worth checking your own address.
Water above 180 mg/L is classed as very hard by the USGS. Where supply is that hard, scale builds on heating elements and tank bottoms, anode rods are used up faster, and relief valves and shutoff valves foul. That is why tank corrosion, crusted connectors and valves and scaled tankless heat exchangers come up so often in this part of Los Angeles County.
| Topic | What we found | Where to check |
|---|---|---|
| Water supply | Walnut Valley Water District serves portions of Walnut. Other suppliers may serve the rest, which we could not verify. | Your water bill, or the district’s service area page |
| Reported hardness (WVWD 2025) | About 234 mg/L (Weymouth supply) and 97 mg/L (Miramar supply) | The district’s 2025 Consumer Confidence Report |
| Permit office | City of Walnut Community Development, Building and Safety Division, at City Hall, 21201 La Puente Road. The city lists (909) 595-7543 for the division and (909) 598-5241 for inspections. | The city’s Building and Safety page |
| ZIP code | 91789 for City Hall. Walnut has other ZIP codes we did not verify. | USPS lookup |
Permits and bracing in Walnut
Replacing a water heater in California normally needs a plumbing permit, and the plumber you hire should say who is pulling it. In Walnut, permits are handled by the city’s Building and Safety Division. Earthquake bracing is part of the work: state law requires new and replacement water heaters to be braced, anchored or strapped. Our water heater replacement guide lists what a compliant installation includes.
Walnut is also a reminder that bracing is not theoretical. The U.S. Geological Survey’s report on the 2008 Chino Hills earthquake, a magnitude 5.4 event, records peak ground acceleration of about 44 percent of gravity at a Walnut station. Few damage reports followed that earthquake, but an unstrapped heater is one of the things that can move in a stronger one.
Common leak scenarios in Walnut and what to do
- Dripping from the pipe beside the heater. Possible thermal expansion or pressure. See relief valve leaks.
- Crusty, damp fittings on top. Often scale and corrosion at connectors. See flex line and valve leaks.
- Water under the tank, dry fittings. Usually a failed tank, so plan for replacement. See tank corrosion.
- Gas smell. Leave first and call 911 or SoCalGas at 1-800-427-2200. See gas safety.
Need a plumber for this? Tell the plumber your Walnut street address so they can confirm they cover it before they schedule a visit.
Call +1 (909) 760-1466Nearby areas
If you are just across a city line, the same guidance applies. See Rowland Heights, where permits run through Los Angeles County, West Covina, where several water suppliers overlap, and Pomona, where Walnut Valley Water District also serves a small area. For a local Diamond Bar plumber, start from the main water heater leak repair page.
Frequently asked questions
Is the water hard in Walnut?
Walnut Valley Water District’s 2025 report lists average hardness of 234 mg/L for one of its main supplies and 97 mg/L for another, so it depends on the blend your street receives. The higher figure is above the 180 mg/L the USGS calls very hard.
Who issues water heater permits in Walnut?
The City of Walnut’s Community Development Building and Safety Division. Ask the plumber to confirm who is pulling the permit and when the inspection will happen.
Who supplies water to my Walnut home?
Walnut Valley Water District serves portions of Walnut. Your water bill names your supplier, and that supplier’s annual water quality report gives hardness and other details.
Do you have a Walnut office?
No. We are a referral service with no public office. We connect callers with independent plumbers who confirm coverage for the address you give.
Sources and further reading
- Walnut Valley Water District: 2025 Consumer Confidence Report
- Walnut Valley Water District: service area
- City of Walnut: Building and Safety Division
- USGS: 2008 Chino Hills earthquake (archived event page)
- USGS Water Science School: Hardness of water
- California Health and Safety Code section 19211 (water heater bracing)
Related guides
- Emergency water heater leak repairWhat to do in the first ten minutes, how to find where the water is really coming from, and when to call right away.
- Leaking from the bottom: tank corrosionHow tanks wear out, what the anode rod does, and how to tell a failing tank from a fitting leak or condensation.
- Replacing a leaking water heaterWhen a leak means replacement, what a California-compliant installation includes, and how permits and bracing fit in.