ok let me do a long Mr. Wilson post here.
Here we go...
Hard water is usually caused by high level of calcium or magnesium. It can cause scale build up in pipes, home appliances etc. Both Calc and Mag can be removed through water purification i.e. RO and distilled. But!!! because they are expensive and water softners are not as much, softening the water is a good first line of action when treating hard water. The harder the water the faster and more damaging it will be to filters and membranes. So you will be replacing them extremely quickly. So not to get crazy scientific but a softner has a resin which look like tiny plastic beeds. This resin acts as a ion exchanger converting the calcium and magnesium to sodium and potassium, which is "softer". So for the exchange to happen the "tiny beads are soaked with sodium and potassium and when the tap water comes through, the calc and mag switch places with the sodium and potassium. Eventually the beads have lost all the sodium and potassium and are covered in calcium and magnesium. At this point the unit regenerates. Thats where the salt comes in. Softner salts are basically pure sodium and potassium. A softner will have a brine tank next to the softner. In there the "salt" will be soaked in water so it slowly dissolves. Then that solution will be sucked into the softner washing away all the calc and mag down the drain and refueling the beads with the potassium and sodium again. Cycle continues and continues.
Why is this a good thing. Well for people in my neck of the woods, you can't live without it. My shower heads will plug in days after I forget to add more salt. Washer, dishwasher and sinks will get damaged due to scale build up. Soap will not suds nicely with hard water, the soap reacts with the high calcium and you can rub your hands with soap all you like and it won't suds.
Why this helps us in the hobby? well having a softner makes your RO membrane job easier. The easier your RO job is, the easier your DI job is. The easier your DI job is, the longer you have 0 TDS water and don't need to spend money changing filters, membranes and resins.
Grains of hardness is a unit of measurement used when calculating how hard water is. It can also be compared to TDS. This information is also going back to the DI issue we talked about earlier and how long they should last. The calculations below should help you better understand why a good RO is important, because it is directly related to how long your DI will last and how dependable your final results will be, no matter what brand of DI resin you have. Hopefully my calculations are not to crazy.
G= grains of hardness
T= TDS (total dissolved solids)
X= gallon useage (how many gallons used - product water)
R= DI resin grains capacity (how much crap a DI can remove until changing)
Our formulas
G = T / 17.1 X = R / G
So for example a good RO should take Oakville water down to 4 TDS. And for example and average sized DI resin has a grains capacity of 900.
G = T / 17.1
G = 4 / 17.1
G = 0.2339
X = R / G
X = 900 / 0.2339
X = 3847.80 gallons
Now the same DI with a RO unit that produces 15 TDS as someone mentioned before.
G = T / 17.1
G = 15 / 17.1
G = 0.8772
X = R / G
X = 900 / 0.8772
X = 1025.99 gallons
You can see the difference. With a unit that has TDS creep, its even more damaging to a DI. Your better off having a cheap RO that makes less water but is consistently on the high side of TDS, roughly 10 etc. A unit that is known to creep is brutal, because you don't know what those first jolts of water are, 50 TDS, 60 TDS etc. Those jolts will really soak up the resins capability fast.
Hope this helps
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