Water Education
Understanding San Diego's water
San Diego has some of the hardest municipal water in the United States. This page explains where it comes from, what makes it hard, and what you can do about it — with facts, not fear.
Origins
Where San Diego's water comes from
San Diego does not have abundant local water resources. The region receives an average of about 10 inches of rain per year — far less than what its population of over 3 million requires. As a result, the San Diego County Water Authority (SDCWA) imports the vast majority of the region's water supply from two distant sources.
The Colorado River
The largest single source of San Diego's water is the Colorado River, delivered via the 242-mile Colorado River Aqueduct operated by the Metropolitan Water District of Southern California (MWD). The river originates in the Rocky Mountains of Colorado and flows roughly 1,450 miles through seven states and into Mexico before reaching the Gulf of California. Along this journey, the water passes through sedimentary rock formations — sandstone, limestone, and shale — dissolving calcium, magnesium, and other minerals. By the time it reaches San Diego, the Colorado River water has accumulated a significant mineral load, which is the primary reason our tap water is so hard.
The State Water Project
San Diego also receives water from the State Water Project (SWP), which collects snowmelt and rainfall from Northern California and delivers it south through 700 miles of aqueducts, tunnels, and pumping stations. SWP water is generally softer than Colorado River water, but it still picks up minerals during its long journey. The proportion of SWP water in San Diego's supply varies from year to year depending on precipitation levels in Northern California and allocation decisions by the Department of Water Resources.
Local sources
San Diego County maintains a network of local reservoirs — including San Vicente, El Capitan, Sutherland, and Hodges — that capture local rainfall and runoff. In a typical year, local surface water provides a relatively small fraction of total supply. The city also operates the Pure Water San Diego program, which is expanding the production of purified recycled water for potable reuse. The Claude “Bud” Lewis Carlsbad Desalination Plant, operated by Poseidon Water, produces approximately 50 million gallons per day of desalinated seawater, accounting for roughly 10% of the region's supply.
The net result is that most of the water flowing through San Diego taps has traveled hundreds of miles through mineral-rich geology before reaching your home. This journey is what makes our water distinctively hard.
Hardness
Why San Diego's water is so hard
Water hardness is a measure of dissolved calcium and magnesium in water, typically expressed in parts per million (ppm) or milligrams per liter (mg/L) of calcium carbonate equivalents. The U.S. Geological Survey classifies water as follows:
| Classification | Grains per gallon | ppm (mg/L) |
|---|---|---|
| Soft | 0 – 3.5 | 0 – 60 |
| Moderately hard | 3.5 – 7 | 60 – 120 |
| Hard | 7 – 10.5 | 120 – 180 |
| Very hard | 10.5+ | 180+ |
Essentially all of San Diego County sits in the “very hard” band. For homes served by the City of San Diego, published figures span roughly 12.5–18 grains per gallon (about 215–285 ppm), varying by neighborhood, the treatment plant serving you, and the seasonal source blend.
Source: City of San Diego Annual Drinking Water Quality Report, 2024.
In North County, Olivenhain Municipal Water District — which serves much of Carlsbad and portions of Encinitas and Rancho Santa Fe — publishes hardness guidance of up to roughly 15 grains per gallon (about 250 ppm), and explicitly recommends those values when configuring a water softener.
Source: Olivenhain Municipal Water District published water quality guidance, 2024.
One important honest caveat: hardness in San Diego County is not one number. It depends on which agency serves your address, which treatment plant is feeding that agency that month, and the seasonal blend of Colorado River water, State Water Project water, and desalinated seawater. Published figures from different sources can disagree by several grains per gallon for the same city. The only way to know your actual hardness is to measure it at your tap.
To put that in perspective, cities like Seattle and Portland typically measure around 20–30 ppm — an order of magnitude softer. Even compared to other California cities, San Diego's water is notably hard: San Francisco's supply from the Hetch Hetchy reservoir measures around 30 ppm, and Los Angeles averages roughly 150–200 ppm depending on the source blend.
The hardness comes primarily from the Colorado River water. As the river cuts through the Grand Canyon and flows across the desert Southwest, it dissolves limestone and other carbonate rocks, accumulating calcium and magnesium ions. Municipal treatment plants are highly effective at what they are designed for — the City's Alvarado and Miramar plants use ozone as a primary disinfectant, a genuinely advanced approach to pathogens and turbidity. But no conventional municipal plant removes hardness or dissolved solids. Those pass through treatment and distribution intact, arriving at your faucet in the same concentration they entered the aqueduct. A home system is not a correction of the city's work; it picks up where municipal treatment, by design, leaves off.
It is worth noting that hard water is not a health concern. Calcium and magnesium are essential minerals, and the levels found in San Diego's water are well within EPA guidelines. The issue is entirely practical: scale buildup, appliance wear, soap performance, and the aesthetic effects on fixtures and glassware.
Disinfection
Chloramine in San Diego's water
Like many large U.S. water systems, the City of San Diego uses chloramines — a combination of chlorine and ammonia — as the primary residual disinfectant in its distribution system. San Diego switched from free chlorine to chloramines in the early 2000s, following EPA guidance aimed at reducing the formation of disinfection byproducts (DBPs) such as trihalomethanes and haloacetic acids.
Chloramines are effective at maintaining disinfectant residual throughout long distribution networks — which is important in a system as large as San Diego's. However, chloramines have a few characteristics that distinguish them from free chlorine:
Persistent taste and odor
Chloramines produce a different taste and odor than free chlorine. Many people describe it as a flat, chemical, or slightly metallic taste. Because chloramines are more stable than free chlorine, they do not dissipate as easily — leaving a pitcher of water on the counter or boiling it briefly will not remove chloramine the way it does free chlorine.
Standard carbon filtration is less effective
Basic granular activated carbon (GAC) filters, like those in many refrigerator dispensers and pitcher filters, are designed to reduce free chlorine. Chloramines require either catalytic carbon or longer contact time with standard GAC to achieve meaningful reduction. This is why many San Diego residents find that their refrigerator water still tastes “off” even with a new filter installed.
Harmless at regulated levels
Chloramines in municipal water are regulated by the EPA under the Safe Drinking Water Act. The levels maintained by the City of San Diego comply with federal and state standards. The taste and odor are aesthetic concerns, not health concerns, and addressing them is a matter of personal preference and comfort.
For residents who want to reduce chloramine taste and odor, the most effective approach is a point-of-entry system using catalytic carbon or a high-volume bed of granular activated carbon with sufficient contact time. Point-of-use options include under-sink reverse osmosis systems, which remove chloramines along with dissolved solids. Our whole-home system uses 14 pounds of coconut-shell granular activated carbon in a configuration designed for chloramine contact time, and our under-sink RO system provides an additional layer of treatment for drinking water.
Effects
What hard water does in your home
Hard water is not dangerous, but it is consequential. The dissolved calcium and magnesium in San Diego's water affect your home in several measurable ways. Understanding these effects helps you make an informed decision about whether treatment is worth the investment for your household.
Scale on fixtures and appliances
When hard water is heated, dissolved minerals precipitate out and form scale — a hard, chalky deposit of calcium carbonate. This happens inside water heaters, on heating elements, inside dishwashers, in coffee makers, and on any surface where water evaporates. In tank-style water heaters, scale accumulates on the bottom of the tank and on heating elements, reducing thermal efficiency. The U.S. Department of Energy notes that scale buildup of just 1/16 of an inch on a heating element can increase energy consumption by approximately 11%.
Tankless water heaters are especially vulnerable. Scale deposits on the narrow heat exchanger passages, reducing flow and heat transfer. Most tankless water heater manufacturers recommend water softening in areas where hardness exceeds 120 ppm — well below San Diego's typical levels. Some manufacturers condition their warranty on the use of a water softener.
Spots on glass and fixtures
The white spots and hazy film you see on shower doors, drinking glasses, and chrome fixtures are mineral deposits left behind when hard water evaporates. In San Diego, these deposits are primarily calcium carbonate with some magnesium and silica. They bond to glass and metal surfaces and become progressively harder to remove over time. Many homeowners resort to specialized acid-based cleaners or professional glass restoration services — recurring costs that softened water largely eliminates.
Effects on skin and hair
Hard water affects the way soap and shampoo interact with your skin and hair. Calcium and magnesium ions react with soap molecules to form an insoluble precipitate — commonly known as soap scum — that does not rinse away easily. This residue can leave skin feeling dry or tight after bathing and can make hair feel stiff, dull, or difficult to manage. Many San Diego residents notice an immediate difference in skin and hair texture after switching to softened water. Soap and shampoo also lather more readily in soft water, meaning you can use less product per wash.
Increased soap and detergent usage
Hard water reduces the cleaning effectiveness of soaps, detergents, and cleaning products. The minerals in hard water bind with surfactants — the active cleaning agents in soap — neutralizing them before they can do their job. As a result, you need to use more soap in the shower, more detergent in the washing machine, and more dish soap at the sink to achieve the same level of cleaning. Studies by the Water Quality Research Foundation found that softened water can reduce detergent usage by up to 50% while maintaining or improving cleaning performance.
Pipe and plumbing wear
Over years and decades, scale accumulates inside pipes, particularly at joints, elbows, and valves where flow changes direction. In copper plumbing — common in San Diego homes built between the 1960s and 2000s — scale gradually reduces the internal diameter of pipes, restricting flow. In older homes with galvanized steel pipes, the effect is even more pronounced, as scale combines with corrosion to significantly narrow pipe passages. While softening your water does not remove existing scale, it stops new deposits from forming and, over time, softened water can gradually dissolve some existing scale deposits.
Solutions
What you can do about it
Municipal water treatment is designed to make water safe to drink — and it does that well. But treatment plants are not designed to soften water or remove the minerals that cause hardness and taste concerns. That is left to the homeowner. There are two main approaches, and they work well together.
Whole-home softening and filtration
A whole-home system installs at the main water line — the point where water enters your house — and treats every gallon before it reaches any fixture or appliance. Our system combines ion-exchange softening resin, which removes calcium and magnesium, with granular activated carbon, which reduces chloramine taste and odor. The system regenerates automatically based on your actual water usage, using salt to recharge the resin bed. This is the most comprehensive approach: every shower, every faucet, every appliance gets softened, filtered water.
Our whole-home system is sized specifically for San Diego water conditions and typical household flow rates. It includes 50 pounds of NSF-certified softening resin and 14 pounds of coconut-shell activated carbon, installed by licensed technicians with professional plumbing connections.
Learn about our whole-home systemUnder-sink reverse osmosis for drinking water
For drinking water specifically, reverse osmosis (RO) provides the highest level of purification available for residential use. An RO system pushes water through a semipermeable membrane that blocks dissolved solids, including the minerals that cause hardness, chloramines, and a wide range of other dissolved substances. The result is exceptionally clean-tasting water delivered through a dedicated faucet at your kitchen sink.
Our under-sink system is a tankless RO unit capable of producing up to 800 gallons per day — far more than a typical household needs, which means water is always available on demand without waiting for a storage tank to refill. It includes a dedicated brushed-nickel faucet and quick-connect fittings for straightforward filter changes.
Learn about our RO systemMany of our customers install both: a whole-home system to protect plumbing, appliances, and fixtures throughout the house, paired with an under-sink RO system for the best possible drinking water. The two systems serve different purposes and complement each other well. The whole-home system also extends the life of the RO membrane by reducing the mineral load before water reaches the under-sink unit.
Sources and notes
Water hardness classifications: U.S. Geological Survey, “Hardness of Water.”
San Diego water quality data: City of San Diego Public Utilities Department, Annual Drinking Water Quality Report (Consumer Confidence Report).
Colorado River Aqueduct: Metropolitan Water District of Southern California.
Carlsbad Desalination Plant capacity: San Diego County Water Authority.
Energy efficiency impact of scale: U.S. Department of Energy.
Detergent usage study: Water Quality Research Foundation, “Softened Water Benefits Study,” 2009.
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