Simi Valley Water Is Very Hard — Here's What It Costs You Each Year

Why Is Simi Valley Water So Hard?

Here’s the short version: Simi Valley’s water isn’t hard because of what’s under the city. It’s hard because of where the water comes from before it ever reaches your tap. Roughly 82% of your supply is treated surface water delivered by the Calleguas Municipal Water District, which buys imported water from the Metropolitan Water District of Southern California. That water originates in Northern California and the Colorado River, and it travels a long way through a lot of rock before it gets to you.

The other 18% comes from local groundwater pumped from the Simi Valley Groundwater Basin. That basin sits in a valley filled with ancient alluvial deposits, which is a fancy way of saying layers of sand, gravel, and clay washed down from the surrounding Simi Hills and Santa Susana Mountains over millions of years. As rainwater and imported recharge percolate through those deposits, it picks up dissolved minerals. The local groundwater tends to run harder than the imported surface water, which is why the blended supply lands at 12.28 GPG, firmly in the “very hard” category.

But here’s the thing about that imported surface water. The State Water Project pulls from the Sacramento-San Joaquin Delta, and the Colorado River Aqueduct draws from Lake Havasu. Both of those source waters pass through and over limestone-rich formations and mineral-laden soils on their journey south. Calcium and magnesium carbonate dissolve readily into water, and by the time that water has crossed hundreds of miles of California terrain, it’s carrying a serious mineral load. The Metropolitan Water District treats the water for safety and clarity, but hardness isn’t something they remove. It’s not a contaminant; it’s just dissolved rock.

So you’re not imagining it. Your water is hard because it’s a blend of two hard sources: mineral-rich imported surface water and mineral-rich local groundwater. Neither one is soft to begin with, and mixing them doesn’t dilute the hardness to a comfortable level. At 12.28 GPG, you’re well above the 10.5 GPG threshold the USGS uses to classify water as “very hard.” For context, the USGS puts the national average around 7.3 GPG, and about 85% of US households have hard water. Simi Valley sits on the harder end of that spectrum.

How Simi Valley Compares to Nearby Cities

If you’ve lived in the Conejo Valley or the San Fernando Valley, you’ve probably noticed your water doesn’t behave much differently than Simi Valley’s. That’s not a coincidence. Much of Ventura County and the surrounding region relies on the same imported water infrastructure. Thousand Oaks, Moorpark, Camarillo, and much of eastern Ventura County all receive water through the Calleguas Municipal Water District, which means they’re drawing from the same Metropolitan Water District supplies that make up the bulk of Simi Valley’s blend.

That doesn’t mean every city in the area has identical hardness numbers. Local groundwater blending varies from system to system. Some cities pull a higher percentage from their own basins, and those basins have different mineral profiles depending on the local geology. A city that relies almost entirely on imported surface water might run slightly softer than Simi Valley, while a city that pumps heavily from a shallow alluvial basin could run harder. But the general character of the water, the mineral load, the way it reacts with soap, the scale it leaves behind, is going to feel familiar across the region.

The USGS classifies anything above 7 GPG as “hard” and anything above 10.5 GPG as “very hard,” so most of the cities sharing Simi Valley’s water infrastructure are in the same broad category. You’re not dealing with an outlier situation. You’re dealing with a regional reality. The EPA doesn’t regulate hardness as a health hazard; it’s purely an aesthetic and nuisance issue under the Secondary Maximum Contaminant Level guidelines. But nuisance is the right word for it. Hard water at this level means scale builds faster in your water heater and on your fixtures, and you’ll go through more soap and detergent to get the same cleaning results.

According to the Water Quality Association, hard water carries a real cost in energy, appliance wear, and cleaning products, and that cost scales with your actual hardness level. The WQA’s industry estimate, roughly $800 per year in 2010 dollars (about $1,230 in 2026 dollars, CPI-adjusted), assumes a typical household at average hardness. At 12.28 GPG, you’re above that average, so your costs run higher than the baseline. Battelle Memorial Institute research found that gas water heaters lose about 4% efficiency per 5 GPG of hardness, and the DOE notes that just a quarter inch of scale can cut water heater efficiency by up to 40%. Hard water also shortens water heater service life by roughly 30 to 50%. That’s the real price of very hard water, and it’s a price Simi Valley residents pay every time they run a load of laundry or take a hot shower.

How does Simi Valley stack up against the rest of California? It's very hard at 12.28 GPG — Oxnard, Ventura, and Berkeley sit nearby with different numbers. See the full hardest-water ranking for context.

See where Simi Valley sits on the California water hardness map →

Want the broader explainer on what hardness actually is and how it behaves? Read hard water vs. soft water, explained.