What is soft/ hard water and why is soft preferred?
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Soft water isn’t as mineral concentrated as hard water. It comes down to preference, but soft water tends to taste better and smoother.
Hard water has a large amount of mineral content in it. The minerals are bad in homes because they can cause plumbing related issues like lime scale buildup in pipes and on fixtures. It’s also rough on things like ice makers, dishwashers, and washing machines.
Hard water also tends to have a taste to it, not necessarily a bad or unpalatable taste, just a distinctly not-water taste.
Hard water can also contribute to skin conditions by leaving some buildup on people after showering. It’s hard to get properly clean when your water is dirty.
So water softeners and filters help to reduce the mineral content of the water to prevent those various things from happening.
Hard water has minerals that are in the water but invisible to the naked eye.
Soft water has fewer of these minerals.
Ever see a water faucet with all sorts of white or green crusty stuff on it, like it looks kinda like a rock growing on your faucet. [Like this](https://imgur.com/a/kZ3APje)
Those are hard water deposits. That stuff builds up inside of pipes, appliances, shower heads and all the things. Some of those are expensive to replace like washing machines, dishwashers, etc.
Since soft water has fewer of those minerals it doesn’t build up as quickly which is why it’s preferred.
Hard water contains a lot of calcium minerals, such as calcium carbonate, magnesium carbonate, and/or calcium sulfate.
These tend to interfere with the action of soaps and detergents.
They can cause visible mineral deposits on glassware and metal cutlery. These are called “hard water spots.”
Certain soaps may react to form insoluble salts with calcium and magnesium. Certain bacteria find such deposits to be palatable. Over time this results in a thin film deposit called soap scum. Note that this isn’t harmful, as disease causing bacteria cannot live very long in such conditions. They’re not adapted to live in that environment.
Over time such minerals may form deposits on taps or shower heads, for example. This interferes with shower heads function causing the spray to be uneven.
(Note however that calcium and magnesium are essential nutrients in the body. So hard water may be slightly more healthy. However there’s generally not enough of either in hard water to fully satisfy daily intake needs.)
Soft water mostly contains sodium and potassium minerals. These are much more water soluble and are less likely to cause deposits. Such deposits can easily be rinsed away due to their solubility. They generally don’t interfere with the action of soaps. Soap scum is less of a problem with soft water.
What is hard water?
Hardness is caused by the dissolved metal salts of calcium and magnesium, usually in carbonate form, along with other metals in lesser amounts. Hard water is found throughout the world. The hardest sources are usually underground where water and rock have lots of time to interact. The rainfall and snowmelt that percolates through the soil into the aquifer starts out soft but contains dissolved CO2. This leaches minerals like calcium or magnesium carbonate out of the rock turning the water hard.
Calcium carbonate, mostly found in limestone, is not very soluble so only a little heat makes it precipitate out. It’s the whitish scale in your kettle and is also found in stalactite and stalagmite formations in caves. Magnesium carbonate is found in a rock called dolomite. It’s very insoluble and ends up in your kettle too. These minerals aren’t harmful to humans or animals but play havoc with hot water heaters, dishwashers, laundry, kettles and even showering.
Hardness is commonly measured in grains, which is a US unit of measure. One grain is equivalent to 64.8 mg of dissolved calcium carbonate in 1 US gallon (3.8 litres). Soft water is 3.5 grains or less. Very hard water is anything over 10.5 grains.
Where I live has some of the hardest water in all of North America at 38.
Water softening
The easiest and most common way of treating hard water is the use of a water softener. The main component is a tank containing tens of thousands of plastic resin beads made of cross linked sodium polystyrene sulfonate. This synthetic chemical (invented in the 1930s) is known as an ion exchange resin and functions to remove calcium and magnesium ions from your water. There’s also a water soluble drug version, without the cross links, used to lower potassium levels in people.
When you turn on a tap or run the shower, hard water flows into the resin tank and comes in contact with the resin beads. Due to concentration gradients, calcium and magnesium ions in the hard water displace atoms of sodium bound to the active sulfonate groups in the resin. The released sodium ions combine with the carbonate ions left behind in the water to form sodium carbonate, Na2CO3. The newly softened water flows from the resin tank’s outlet, through the supply lines and out to the tap.
Sodium carbonate is also known as washing soda, a centuries old household cleaner and laundry additive. It’s thousands of times more soluble in water than calcium or magnesium carbonate. So it won’t precipitate out as scale or interfere with your soap which is great news for your plumbing, dishwasher and washer, water heater, kettle and even washing up. Softened water does have slightly elevated levels of sodium but not enough to cause danger. It affects taste though and I prefer hard water for drinking.
The resin in your softener can only soften so much water. At some point all the sodium ions will be exchanged and your softener will no longer function. Back in the old days (I remember this) you’d call to have the tank swapped out but nowadays all you need to do is run the recharge cycle on your machine.
Recharge timing is automated on modern machines using a flow meter that measures how much water you have used. Older softeners use a clock timer that would be set to recharge every few days, wasting a lot of salt and water. The recharge is usually set to run in the middle of the night when no one is turning on taps or flushing toilets.
The recharge cycle has a number of stages and takes a few hours to finish. The most important part of this for today’s explanation is the brine cycle. Water softeners have a salt tank that stores up to 100 kg of salt. It is partially filled with very salty water. Brine is drawn from this tank into the resin tank and, due to the very high concentration of sodium, reverses the ion exchange on the resin beads I’d mentioned earlier. The calcium and magnesium form salt compounds with the chlorine from the brine and are washed down the drain into the sewer.
After the resin is refreshed with sodium ions (and rinsed) the last step is the refill cycle on the brine tank. Fresh water is pumped into the tank which dissolves some more salt for the next recharge. So every few weeks you’ll need to add some salt to the tank. It’s a special high purity salt made just for softeners so don’t use anything else. 20kg bags are somewhere around ten bucks give or take.
Water is “nature’s solvent” and is efficient at collecting debris on a molecular level. “Hard water” has minerals in it, which means the water has already collected debris. “Soft water” has this debris removed, which makes it better at cleaning again. Most cleaning agents, such as laundry soap, are mostly made of chemicals to soften water so that the actual soap in the cleaner will work with hard water. Soaps made for soft water don’t include these agents, which is why you don’t need to use as much of these soaps. Soft water soaps don’t work well with hard water.
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