When to change the Brita cartridge?

100% to 0%
The Rocket Giotto espresso machine at my girl friend's place uses water from a Brita filter. This filter has a timer that counts down from "100%" to zero over a number of weeks but that time span is totally unrelated to the actual use of the filter so it's useless as a reminder to change the filter cartridge for a fresh one.

Unpredictable
I reset the timer a few times before replacing the filter but then I mostly forget how often I have reset it and I take out a new cartridge when I start to feel worried about the water hardness, which is subjective and unpredictable.

Brita themselves suggest replacing it every two months or after every 40 gallons of water taken from the pitcher although local water hardness may vary greatly and thus influence the life span of a filter cartridge. So that's not a great help either.

It would be nice if Brita supplied a test kit to see when the water quality delivered by the filter is deteriorating.

Predicting
For those who want to skip the tests below, a short and simple conclusion: find a GH droplet test for aquariums, one that measures 1ºdH per droplet in a 5ml test tube. If it takes more than 5 droplets for the water to change color, replace the cartridge. It's a cheap test too.

For more in-depth info, read on...

There's information about aspects of water hardness here:

  1. http://en.wikipedia.org/wiki/Water_softening 
  2. http://en.wikipedia.org/wiki/Carbonate_hardness
  3. http://en.wikipedia.org/wiki/DGH


Test kits
This morning after coffee I took out a few test kits that I have:
  1. HM Digital EC/TDS/TEMP COM-100 water quality tester
  2. Velleman digital pH meter
  3. "Raw Water Hardness Reagent" measuring TH from Advantage Chemicals
  4. Tetra Test GH drop test 
  5. Tetra Test KH drop test


Water samples
I filled three bowls with water:

  1. Water from the tap, unfiltered
  2. Water from a used Brita filter
  3. Water from a brand new Brita filter

All three samples were 16ºC:

test set up

These were the results:


The ppm does not change much because a resin based filter like the Brita replaces most Ca ions (which can cause scaling over time) with Natrium (sodium) or Magnesium ions. Basically, harmful particles are replaced with harmless ones and the total count of particles does not change drastically.

To get zero ppm, one would need an osmosis type filtration (and then add the elements we want for fine coffee extraction later).

I was a bit surprised that the TH droplet measurements seemed more in proportion to the GH results than parallel the measured KH values.

I did the KH test twice to be sure, the second time using 10ml instead of 5ml so 1ºdH difference was then indicated by two drops of reagent.

Conclusions
Apparently, in these tests at least, a filter that has been used for a while can still be effective in lowering the KH substantially even though the GH (drastically lower at the onset) is already increasing.

The TH droplet technique is equally helpful as the GH to check the current effectiveness of the filter cartridge.

70-140 ppm is said to be "medium hard water" and fine for the espresso machine, so the "old" filter that I just replaced could have been used longer.

Quick and easy test?
The electronic ppm meter is useful and convenient as it shows a significant difference between unfiltered water and a brand new or used-but-okay filter. Using it I'd say: replace the filter if it reads a ppm above 325. You'd be on the safe side, still be a long way from the unfiltered water quality.

The Velleman digital pH is not useful for this cartridge testing. It merely measures a marginal difference between samples and does not separate an old (but still good) filter from tap water.

Also, if I want to take the time to set up a droplet test, just one type of droplet test, either the TH or the GH, would tell you enough.

The GH droplet test is the cheapest. I paid about 6 Euros for it, whereas the digital ppm meter was around 80 Euros (plus I bought special calibration fluid to ensure it is working perfectly in the range that I am testing).



Reacties

patricia zei…
Zeer mooie website. Heeft u mooi gemaakt.
Frans zei…
Dank u wel!

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