# What PPM is your harvested rainwater?



## Tempted (Oct 8, 2012)

I've just set up my own rainwater harvesting system having seen numerous good ones on here. I'm yet to use it yet, as I only set up the 3 butts recently and they hadn't filled the last time I washed my car at the weekend. Looking outside today though, I am certain they will be brimming with lovely soft water ready for my next wash!

Anyway, I did dunk the old TDS tester in last week and observed a reading of 10ppm. I don't know if my expectations might have been unrealistic, but I thought I'd get 0ppm. That being said, my household water is 495 and so this will be an amazing improvement when I use it.

What do you guys get where you live? Is 10ppm considered low enough for spotless drying? I do actually have an unused DI vessel I bought a few years ago which would take the edge off, but the PW wiring is all plumbed in now, so that would be a bit of work.


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## voon (Apr 28, 2010)

TDS doesn't measure calcium carbonate ... these cheap TDS meters will probably not give you a ton of accuracy first and secondary, mesure whatever solids, so you'll have fine sand particles, algae, whatever in the water.


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## Tempted (Oct 8, 2012)

What's the best way to measure it, in that case?


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## voon (Apr 28, 2010)

Nothing in the cheap range ... proper CaCO3 meters are very expensive, often in the multi hundred. Maybe the strips sold for water hardness are more accurate for CaCO3, but I'm not sure there myself.


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## Tempted (Oct 8, 2012)

Would have been interesting to know, but I guess trying it will prove whether spotless drying can be achieved. Others seem to say their water does, so that bodes well. In some ways the measurement is immaterial really.


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## percymon (Jun 27, 2007)

If the car is cleaned, then rained on and left to dry - do you get water spots ? 

Theoretically you should get the same from the water butts assuming you are turning over the contents at a reasonable rate.


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## steelghost (Aug 20, 2015)

My collected rainwater reads in the mid 20s on my cheapo TDS.

Anecdotally, I get _negligible _(but not nil) water spotting.


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## voon (Apr 28, 2010)

percymon said:


> If the car is cleaned, then rained on and left to dry - do you get water spots ?
> 
> Theoretically you should get the same from the water butts assuming you are turning over the contents at a reasonable rate.


Not neccessarily exactly the same, since direct rain can wash the air (Pollen, Sahara sand etc), which deposits on the car, while in the watertank of a harvesting system it may settle down etc.

If I'd use rain water, I'd make sure th tank is impenetrable for sunlight (to avoid photosynthesis by algae etc) and use a simple filter on the outlet, that allows enough waterflow, but keeps back the worst.


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## Tempted (Oct 8, 2012)

voon said:


> Not neccessarily exactly the same, since direct rain can wash the air (Pollen, Sahara sand etc), which deposits on the car, while in the watertank of a harvesting system it may settle down etc.
> 
> If I'd use rain water, I'd make sure th tank is impenetrable for sunlight (to avoid photosynthesis by algae etc) and use a simple filter on the outlet, that allows enough waterflow, but keeps back the worst.


Thanks for your insight. Do you think a standard water butt (green plastic with removable black lid), will be sufficiently UV protected?

In terms of filters, there is a coarse one on the rain water diverter and a 50 mesh on an inline filter. Hopefully along with the natural filtration that occurs between the 3 butts, this will be sufficient.


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## voon (Apr 28, 2010)

Hard to say how much growth it can cause ... I don't know of any tests  But basically any light passing will let plants grow.


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## Tempted (Oct 8, 2012)

steelghost said:


> My collected rainwater reads in the mid 20s on my cheapo TDS.
> 
> Anecdotally, I get _negligible _(but not nil) water spotting.


Bodes well. Both our cheapo TDS could be telling us anything anyway 🤣


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