My soil pH is 7.7, tested by EarthCo. (drgoodearth.com). I'm next to a limestone quarry. My soil has lots of limestone and dolomitic stones. The soil test came back: very high in magnesium, but short on calcium, phosphorus, and potassium. The calcium forms INSOLUBLE complexes with the excessive magnesium in the soil. University of Colorado Extension has a good article explaining how phosphorus is also NOT available in alkaline soil due to its forming complex with calcium. Gypsum is safe to use in alkaline soil to provide calcium without raising your pH further.

Found a fantastic link which explains the many forms of calcium: http://waltsorganic.com/ag-lime-dolomite-gypsum-oyster-shellwhat-kind-of-calcium-do-you-need/ Agricultural Lime: Calcium carbonate – CaC03 Pure calcium carbonate is used to help prevent the spread of various diseases, such as powdery mildew, black spot, and blossom end rot ... Adding Ag. Lime to your soil will also raise your PH making it more alkaline. Dolomite: Dolomitic Lime contains calcium carbonate, bringing benefits similar to Ag Lime, while also providing magnesium which is important for plants’ utilization of nitrogen, phosphorus and sulfur. Having an excess of magnesium in your soil can cause a break down in soil structure, resulting in hard compact soils. Gypsum: Calcium sulfate, or Sulfate of Lime – CaS042H20, due to its sulfur content Gypsum does not raise the soil PH like lime, and there is some debate as to whether it lowers soil PH. Gypsum helps liberate potash for plant use. Gypsum can also help break up compact and clay filled soils by correcting excess amounts of magnesium in your soil. Oyster Shell Flour: in addition to a large percentage of calcium carbonate, Oyster shell flour contains about 1-% phosphoric acid, which makes oyster shell flour a source of both lime (calcium) and phosphorus. Oyster shell will also slightly raise your soils PH over time. **** From Straw: The horse stable nearby me uses oyster shell lime to deodorize their horse manure. I tested the horse manure pH, and it's over 8. When I applied to my roses, alkaline horse manure (high in calcium & magnesium & potassium & phosphorus) REVERSED blackspots on roses by pumping out new & clean leaves and neutralize the acidity of rain water. Shell lime is best for alkaline clay which needs more phosphorus, plus it raises the pH slowly. Agricultural lime is best to sprinkle on leaves of roses, it's calcium carbonate which is a fungicide, it kills fungus by raising the pH. Dolomitic lime is best for acidic sandy / loamy soil. It will raise the pH, plus supply calcium and magnesium. Magnesium is the "glue" that holds soil together, and is less available in sandy soil. Gypsum also release calcium fast, but doesn't result in pale roses due to 17% sulfur in gypsum. My preference for my alkaline clay: I use shell lime (in horse manure) for heavy-bloomers BEFORE RAIN, and gypsum for wimpy own-roots BEFORE RAIN. Below site sells organic stuff cheap with 5,000 items to choose: 50 lb. of alfalfa pellets for $25, alfalfa seeds, clover seeds (for nitrogen), $9 for 50 lb. of gypsum, $10 for 50lb. of oyster shell lime, $9 for 50 lb. of dolomite lime (best for sandy or loamy soil, since magnesium is the "glue" that retains nutrients). http://www.groworganic.com/search#q=alfalfa hay&p=1 If someone has sandy or loamy soil, the acidic rain will beat up on roots, cause leaching of calcium & magnesium & potassium ... thus leaves become thinner and break out in fungal diseases. I successfully reversed blackspots & mildew on roses just by topping with ALKALINE & HIGH MINERALS & SLOW-RELEASED mulch, such as alfalfa hay (less acidic than alfalfa meal), my dolomitic clay, or horse manure (with oyster shell for calcium & phosphorus for my alkaline clay). Below are some pics. of own-root Golden Celebration. The first one was 2012 pic. in the front of my house, late August 2012: Second pic. below is the base of Golden Celebration, which is 100% clean with horse manure, pic. taken late October 2012 after the 1st frost: Third pic. below is Golden Celebration bloom with horse manure. Golden Cel. got too big for my front walk-way .. when I moved it, there's at least 1 foot of fluffy horse manure, and the root was huge:

The gypsum doesn't actually raise the pH in most soils. However, it's still a good amendment for two reasons. The problem most plants have in very acidic soils is that plant toxic aluminum is soluble when the pH is below approximately 5.4. The sulfate from gypsum combines with aluminum, making it less phyto-toxic. Second, gypsum supplies soluble calcium, often lacking in highly acidic soils, to plant roots.

Good question, I'll have to look at the bill I guess? I live in Hollywood, so it's definitely DWP. I looked at their website and didn't see anything about districts. I assumed most of my water came from their main ____ (whatever it's called, the place where the water comes from), not the Valley one, though come to think of it, I think they mix it all together? I know there's some groundwater mixed in with the imported stuff. I really only maybe skim those reports. They're very interesting, it's just there's so much going on.