Course:EOSC311/2022/Hard vs. Soft Water in the San Francisco Bay Area

From UBC Wiki

Water hardness can have a big effect on a geographical location due to the major role water plays in society. While California water as a whole is considered very hard, two of the main cities of the Bay Area, San Francisco and San Jose, have drastically different hardness levels of their water, despite only being about 80 kilometers (50 miles) away from each other.[1] This may lead to a slightly increased or decreased risk or mortality rate for certain diseases, however more evidence is still needed. Due to the higher concentration of minerals often found in hard water, specifically magnesium and calcium, this may lead residents of San Jose, which has a high average hardness level, to be at a lower risk for deficiency of these minerals, due to water supplementing their dietary intake.

A map of the San Francisco Bay Area, including the cities of San Francisco and San Jose

Statement of connection and why you chose it

I’m from the Bay Area and lived there my entire life before moving to Vancouver. Water in general is an interesting topic in California because we’ve either been in a drought or recovering from a drought for over a decade now. When I moved to Vancouver, I noticed a slightly different “taste” of the water compared to the water from back home. When I began researching water hardness, I noticed the immense difference in hardness levels between two of the major cities of the Bay Area. When we initially began studying water and water hardness, I assumed water hardness would be relatively consistent in places geographically close to each other, however that isn’t always the case. I’m also very interested in how one’s environment influences their health. Physiology is an interesting topic to me, especially because it can be affected by so many different things, that it can be difficult to narrow down what is affecting it and why. In the instance of water hardness, it may be affecting people’s risk of certain diseases or even the mortality rate, depending on where they live.

Hard vs. Soft Water

Scale buildup from hard water in a pipe.

Water hardness is defined as the amount of minerals dissolved in water, specifically calcium and magnesium. Hard water will have higher concentrations of calcium and magnesium than soft water. If an area has hard water, it’s most likely because they’re using groundwater, which picks up minerals from rocks and soil as it flows under the ground. Calcium and magnesium both easily dissolve in water, making it very common for groundwater to contain these minerals.

While magnesium is present in hard water, and sometimes other minerals as well, the typical measurement classifications are based off of the amount of calcium carbonate in the water:

  • Soft: 0 - 60 mg/L
  • Moderately hard: 61 - 120 mg/L
  • Hard: 121 - 180 mg/L
  • Very hard: > 180 mg/L

Hard water can cause many problems for people who use it every day, especially in factories or other places using large quantities of water. Over time, calcium carbonate solids can build up, leading to what is known as scale buildup. Scale buildup can occur in anywhere from electric water heaters, to pipes, to coffee makers. This can lead to reduced efficiency in all of these things, and often leads to people needing to use an acid rinse, such as vinegar to clear it out. For example, in pipes that carry water, the calcium carbonate builds up along the sides, “just as in the human body where blood vessels can be reduced in inside diameter due to cholesterol buildup.” This can lead to decreased water pressure and damaged pipes. While hard water doesn’t have any immediate detrimental effects, it can cause delayed efficiency and some problems over time when used repeatedly without a water softener.[2]

Out of all of California, San Jose has some of the hardest water with a water hardness of 320 mg/L and San Francisco has some of the softest water with a water hardness of 47 mg/L.

Water Sources

The reasoning for the difference in water hardness between San Francisco and San Jose is that they primarily get their water from two different types of sources.[3][4] San Jose gets the majority of their water from groundwater, or more specifically the Santa Clara valley aquifer.[4] San Francisco, on the other hand, gets their water from two watersheds, or areas where surface water collects and flows into a stream or larger body of water.[5] The majority of San Francisco’s water comes from the Tuolumne watershed, which includes the Hetch Hetchy reservoir, Cherry Lake, and Lake Eleanor. The rest of San Francisco's water comes from the Alameda and Peninsula watersheds.[3]

A diagram of an aquifer, showing how it's accessed and recharged.

An aquifer is an underground rock or sediment with enough space for water to flow through. Some substances that can act as aquifers are “unconsolidated materials [such as] gravel, sand, and even silt, [such as] sandstone...[or] other rocks if they are well fractured.”[6] There are confined and unconfined aquifers, where confined have a confining layer separating it from the ground surface, and unconfined don’t. A confining layer is an aquitard (a layer of rock with insufficient permeability to allow for water flow), which prevents water from reaching the aquifer as quickly as it would reach an unconfined aquifer.[6]

As mentioned above, the city of San Francisco gets its water from watersheds, rather than an aquifer. The main watershed is the Tuolumne watershed which is located in Yosemite National Park. However, Yosemite is about 270 kilometers (or 170 miles) away from San Francisco. In order to get the water to the city, it’s carried by the Hetch Hetchy water system. This system is “a 167-mile, gravity-driven network of dams, reservoirs, tunnels, pump stations, aqueducts, and pipelines that collects Tuolumne River runoff on federal land near the Yosemite Valley and transports it to the San Francisco Bay Area.”[7] Overall, the main reason why San Jose has very hard water and San Francisco has soft water is due to the difference in water storage. San Francisco gets its water from an above ground source, whereas San Jose gets their water from below the ground. This leads to the dissolution of minerals, and therefore hard water.

This is also relevant to California's consistent declarations of drought due to relatively low rainfall. San Jose relies on its own rainfall to recharge its aquifer, so during years of less rainfall, they’re more likely to have water restrictions placed on them. However, San Francisco gets their water from much further away, where there is greater rainfall and melted snow to replenish the water source, leading to San Francisco often having fewer and less extreme water restrictions, even when they’ve had low rainfall.[3]


Cardiovascular Disease

Overall, hard water is considered to pose no major health risk for those regularly consuming it. However there are some hypothesized benefits of regularly drinking hard water. One of the better known predicted benefits is the decrease of cardiovascular disease in populations who drink hard water. However, there is no hard evidence (pun intended) for this claim to be substantiated. There have been many studies that suggest drinking hard water, or water with high levels of magnesium leads to lower instances of cardiovascular disease or lower mortality rates in people with cardiovascular disease. However, these results haven’t been replicated and are difficult to attribute solely to the hardness of the water they were drinking. There have been many hypothesized mechanisms, such as the high levels of magnesium having “anti-stress actions against coronary heart disease.” There has also been some evidence to suggest greater levels of calcium can lead to lower blood pressure.[8]

Other Health Effects

Similar to cardiovascular disease, there have been some studies suggesting a connection between water hardness and cancer, but nothing definitive. The few studies that have come out have found links between water hardness and reduced instances of cancer, specifically gastric, rectal, pancreatic, colon, esophageal, and ovarian cancer.[8]

While very few studies have actually been conducted, there have been hypothesized links between hard water and an increased risk of neural tube malformation, Alzheimer’s disease, diabetes, atopic dermatitis (AKA eczema) in children, kidney stones, and reproductive health in men. On the other side, there has been hypothesized connections between the high levels of minerals in hard water and decreased levels of constipation, and eclampsia in women.[8]

Mineral Contributions to Diet

While the majority of mineral intake typically comes from food, or occasionally supplements, small amounts of total mineral intake can come from hard water, if regularly consumed. The levels of calcium in water can contribute to the recommended intake level. However, the recommended intake of magnesium is much lower than calcium suggesting that if there is enough magnesium in water, it may give someone all of their recommended magnesium intake for the day. There has been some evidence to suggest that living in areas with hard water leads to greater bone density, however more evidence is needed to conclude anything.[8]

Effects of Water Softeners

Many people who live in areas of hard water may use a water softener. While most public water systems soften water by precipitating and filtering the magnesium and calcium out of the water, many home water softeners use sodium. Home water softeners will use an ion exchange to replace the calcium or magnesium in hard water with potassium or sodium. If it replaces the ions with potassium, there isn’t much of an issue, however there may be more concern if it utilizes sodium. The levels of sodium in softened water aren’t enough to cause serious health problems in healthy people, however people who are advised to reduce their sodium intake may want to reconsider softening their water, or which softener they use. This may also be important for someone who consumes a high sodium diet, due to the negative health effects sodium can have, most notably hypertension.[9]

Toxic Effects of Chrome

More specific to San Jose is the possible effects of chromite ore. It has been mined in certain areas of the San Francisco Bay Area, including San Benito County, which is just South of Santa Clara county, where San Jose is located. There have been suggestions that the mining of this ore has led to increased levels of chrome in the groundwater, which is highly toxic to plants and humans.[10]

Effects on Agriculture

There are some indirect effects on one’s health due to hard water as well. Hard water is more difficult for plants to absorb, and makes it difficult for plants to get the proper nutrients from the soil. This will often lead farmers to overcompensate by giving the plant more water, which can further lead to decreased nutrients in the plant. Hard water can also lead to increased salinity of the soil. This may be remedied with regular rainfall, as it flushes out the salt, however this is unlikely in places like San Jose that receive relatively little rainfall throughout the year. The salts then build up, leading to hardened soil, which further prevents nutrients from reaching plants, or may prevent plants from growing at all.[11]


As mentioned above, it is possible to get a water softener if you live in an area with hard water. For your home, this is done through an ion exchange and replaces the magnesium and calcium with either potassium or sodium. Hard water doesn’t have any detrimental health effects, so it isn’t necessary to get a water softener for your health. However, water softeners can be a convenient choice for other reasons, as the scale buildup can be difficult and costly to deal with. Hard water may also be difficult to clean with, as it may react with soap and detergent to form a “soap scum,” a type of residue on dishes, laundry, and even hair. This can lead to reduced effectiveness of equipment or reduced quality of clothing.[2]

Conclusion / Your Evaluation of the Connections

A map of the Hetch Hetchy water system that acts as the primary water source for San Francisco

Hard water doesn’t have any severe health effects according to current research, however there are some predicted links to several diseases, including positive and inverse relationships. The most notable one is a possible link between hard water and decreased risk and decreased mortality from cardiovascular disease. Hard water may lead to negative agricultural effects or inconveniences around the house, but these may be prevented with a water softener. However, these aren’t always recommended for those with a high-sodium diet or those at risk of developing hypertension. For residents of San Francisco and San Jose, two cities fairly close to each other geographically but with a wide disparity in water hardness, this doesn’t mean too much for their physiology. Residents of San Francisco don’t need to worry about scale buildup or whether or not to get a water softener, however residents of San Jose may be less likely to have a calcium or magnesium deficiency. This is due to San Francisco getting their water from watersheds, which are above ground, and San Jose getting their water from an aquifer, which is underground. I have a new understanding of water hardness and the possible direct and indirect effects it could have on someone’s life. I also have a new understanding of how small certain factors can seem, but still affect many aspects of one’s life.


  1. "California". Hydroflow USA.
  2. 2.0 2.1 "Hardness of Water". United States Geological Survey.
  3. 3.0 3.1 3.2 Jung & Sumida, Yoohyun & Nami (June 2, 2021). "Here's where the Bay Area's water actually comes from, and what to expect during California's drought". San Francisco Chronicle.
  4. 4.0 4.1 "Groundwater Supply". Valley Water.
  5. Panchuk, Karla (2017). Physical Geology. BC Open Textbooks.
  6. 6.0 6.1 Earle, Steven (2015). Physical Geology (2nd ed.). BC Open Textbooks.
  7. "Hetch Hetchy water and the Bay Area Economy" (PDF). Bay Area Economic Forum. October 2002.
  8. 8.0 8.1 8.2 8.3 Sengupta, Pallav (2013). "Potential health impacts of hard water". International Journal of Preventive Medicine. 4: 866–875.
  9. Bradshaw & Powell, Michael H. & G. Morgan (2002). "Sodium in Drinking Water" (PDF).
  10. Stoffer, Philip (2015). "Rocks and geology in the San Francisco Bay Area" (PDF).
  11. "Solving residential & agricultural hard water problems". Watson Well. October 4, 2019.

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