Why Is My Water So Hard?!?!?

 

Calcium
©2011 Inorganic Ventures, Inc.



Magnesium
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Who among us that live somewhere the water is hard haven’t asked that before ourselves? I certainly have, and I know why the water is hard.  It’s usually more a rhetorical cry of frustration than it is a cry for answers, but none the less, I thought someone out there might want to know a bit more about water hardness, both actual and perceived, so hold on to your hats, because here we go.  Water hardness is defined as the concentration of polyvalent cations, and is expressed as the equivalent concentration of calcium carbonate (CaCO₃) in mg/L.  Huh?  A cation is just an atom or molecule that has a positive electric charge and polyvalent means the positive charge is greater than +1.  So, for example, an atom of calcium dissolved in water is a polyvalent cation because it has a charge of +2, and is shown like this: Ca⁺².  Simple!  The most common polyvalent cations in drinking water that make up hardness are calcium (Ca⁺²) and magnesium (Mg⁺²), but can also include a whole host of ions such as iron, copper, zinc, nickel and others.  These latter elements are usually present in small enough quantities that they do not appreciably add to the hardness, however, so for the most part we can just consider calcium and magnesium.  The quantities for all these polyvalent cations that are included in hardness get converted to equivalent concentrations of calcium carbonate for simplicity and ease of comparing one sample to another.  Consumers like you and I for the most part don’t care about polyvalent/polyshmalent, cat-ions/dog-ions – all we care about is the spots on our glasses and that crusty stuff on our faucet.  Although hardness is a large part of that, it’s also affected by another measurement known as Total Dissolved Solids, or TDS.  That measurement is a bit easier to understand and is pretty much just as its name implies; it’s a measurement of all the stuff dissolved in the water.  It includes hardness, because the calcium and magnesium cations are a dissolved solid and therefore get included in TDS.  But it also includes things like sodium (Na⁺¹), sulfate (SO^-4), potassium (K⁺¹), chloride (Cl^-1) and others that can lead to those dreaded spots and crustiness when water is allowed to dry on glasses or fixtures, leaving the dissolved solids behind.  Many people also think of these compounds collectively as “salt”, and indeed when they dry, they do form salts such as the one we all know, sodium chloride or table salt, but also salts such as calcium sulfate or potassium chloride.  But fixture deposits and spotted dishes aren’t the only problems excessive hardness and TDS cause.  Over the years, calcium, magnesium, and TDS compounds can precipitate out of the water and form a coating on the insides of pipes in the distribution system or in home plumbing systems reducing the flow of water.  These precipitates can also collect in water heaters, reducing their efficiency, or plug up faucet aerators.  On the plus side, there have been some medical studies showing that the calcium and magnesium in hard water can be a significant part of the dietary intake necessary for good health, and that it can even be effective in lowering the incidence of cardiovascular disease.  Other medical studies have been inconclusive on this last point, so the jury is still out.   General hardness ratings are shown in the Table.  Where does all this stuff in the water come from?  For groundwater, the minerals in the water are those that have been dissolved from the local rocks and soils as the water moves through the aquifers beneath our feet.  Calcium, magnesium, and all the rest are very common in the local geologic structures, and water, being such a good solvent, is very effective at removing them.  Surface water, such as that in the California State Water Project, does not come in contact with rocks and soil for nearly as long as groundwater, so it has fewer of these elements dissolved in it, and therefore isn’t as hard.

Orange County Water District Groundwater Adventure Tour



Microfiltration units

Yesterday, November 10, 2011, the Orange County Water District (OCWD) held its annual tour of the Groundwater Replenishment System (GWRS), a state of the art system in Orange County, CA for recycling wastewater into drinking water and maximizing groundwater recharge from naturally occurring run-off in the Santa Ana River watershed. I was lucky enough to get a seat on the tour, which always seems to fill up fast, and along with about 150 other people, participated in the day long adventure.



Reverse osmosis cartridges



The GWRS is the world’s largest advanced wastewater purification system for indirect potable reuse.(1) The wastewater is purified using microfiltration (MF), reverse osmosis (RO), and advanced oxidation (AO) with hydrogen peroxide and ultra-violet (UV) light. The water that results meets all state and federal safe drinking water regulations for potable water. On the tour, they give you the opportunity to drink some, which I did; it tasted good, and I’ve had no ill effects, I assure you. However, rather than being used as a source of potable water directly, the water is either pumped into the ground near the coast as a barrier against seawater intrusion, or it is pumped to percolation basins so it can recharge the groundwater aquifer that underlies a large part of Orange County. The plant has a capacity of 70 million gallons per day (MGD). A 30 MGD expansion is currently in the planning stages, to be completed by 2014; and another 30 MGD expansion is planned for the future.



The far tap is the fully treated wastwater. Yummy!



The aquifer is also recharged by water draining from the Santa Ana River watershed. This recharge is enhanced by the use of rubber dams to divert the water into off-channel percolation basins, and by in-channel engineering that spreads the water out across the entire channel, maximizing the wetted area of the channel, which in turn maximizes percolation. The tour included a visit to one of the rubber dams and related off-channel features. These recharge efforts also include hundreds of acres of constructed wetlands in the area above Prado Dam, one of two large permanent dams on the river. These wetlands take water that drains from heavily agricultural areas, including large dairy farms, which is very high in nitrate, and allows natural biological attenuation to occur. The water leaving these wetlands, which flows into the recharge areas mentioned previously, has nitrate levels that are frequently non-detectable. This process prevents high nitrate water from percolating into the aquifer and causing widespread contamination. The tour group helped plant trees in the wetland area to help prevent erosion.

Inflatable rubber diversion dam on the Santa Ana River

The combination of the GWRS and the other recharge operations puts 230,000 acre-feet (AF) of water back into the aquifer every year; that’s almost half of the 500,000 AF of water that is used within the Orange County Water District.

It was a great tour, and a very educational day all around. I’d highly recommend it to anyone with an interest in water.

(1) The information is from the tour itself, and printed materials that were handed out.

Lead and Copper Sampling for Drinking Water Utilities

Lead & Copper sampling for drinking water systems is very unique in how the samples are taken; how they are reported; and how the data is used.



Lead
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For the most part, lead and copper samples are collected every three years. But, unlike the rest of the samples we are required to take, lead & copper samples must be collected by the customer, since they can only be collected from a tap inside the customer’s home. The tap it is collected from cannot have been used in the previous 6 hours, there can’t be a water softener on the system, and the customer must collect a full liter of water for the sample to be valid. Needless to say, asking your customers to do all of that can be problematic. Samples have to be collected this way because the lead & copper regulation is designed to test premise plumbing, and most lead & copper in peoples drinking water comes from either home fixtures, lead solder in old plumbing, or lead service lines. Every customer who provides a lead & copper sample receives a letter detailing what the results were for the sample taken from their home, as well as a lot of additional information about these elements that is mandate by the U.S. Environmental Protection Agency (EPA).



Copper
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There isn’t really a pass/fail for individual lead & copper samples, and there is no Maximum Contaminant Level (MCL) for this type of sampling. Instead, the regulations have an Action Level (AL) of 0.015 mg/L for lead, and 1.3 mg/L for copper. If the 90th percentile level for the lead & copper samples taken is above the AL, then the regulation requires that the water system take corrective action. Now, what the heck is a 90th percentile level? The 90th percentile means that 90% of the samples are less than that level, and 9% are greater. You determine the 90 percentile level by multiplying the number of samples you take by 0.9; so if you take 20 samples, then sample 18 is your 90th percentile sample. Then you put all the samples in order from least to greatest, and the value of your 18th sample is your 90th percentile level. Phew! Statistics makes my head hurt.

If a system exceeds the AL, then there are certain actions they have to take. These include a public education program about the health effects of lead & copper; implementation of corrosion control in the distribution system; and a lead service line replacement program where applicable. The health effects of lead include neurological damage in children, as well as high blood pressure and reproductive problems in adults. Excessive copper can cause liver and kidney damage in children, and various problems of the digestive system in adults.

If you would like to read more about the lead & copper rule, go to EPA’s web site at this address: http://water.epa.gov/lawsregs/rulesregs/sdwa/lcr/index.cfm