Help me make my own water filter.
June 24, 2011 2:19 AM   Subscribe

Brita filters seem expensive and wasteful. Instead, where can I buy my own cation exchange resin (preferably in the UK)?

I've started enjoying white and green tea, and I think I'm ready to go one step further and filter London's tap water to get better results. To remove the chlorine in tap water, activated carbon seems to be the weapon of choice, and is readily obtainable online. Now, to soften the water, it appears that Brita filters use cation exchange resin, which I can only find in industrial quantities online. Are there any places where I could buy smaller amounts?

My motivations for doing this rather than buying a Brita filter would be:
  • much cheaper
  • less plastic
  • way more fun
  • since it's not enclosed in a plastic box, I could boil* the activated carbon to sterilise it and renew it
  • After a couple months, I could retire the activated carbon and use if for other things
Having said that, alternative solutions will be welcome as well.

* Is it a good idea to microwave activated carbon? If it's good for sponges, it should be good for charcoal, no?
posted by spaghettification to Food & Drink (11 answers total) 6 users marked this as a favorite
 
In addition to activated carbon and an ion exchange resin, Brita uses silver as a disinfectant.
posted by Blazecock Pileon at 2:40 AM on June 24, 2011


Could you open up the filter and use the innards? We use Brita filters and I love the grains. I cut the dead cartridges open, dry the innards and store them in a jar to look at and play with (yay, sand!) - it never occured to me I could sterilise and reuse them, I'd be really interested to hear how I could make my own filters.
posted by freya_lamb at 2:49 AM on June 24, 2011


Im am not sure I follow your plan to boil and reuse the filter material. I have always understood filters to work by gradually getting gunked up and full of all the minerals they've taken out of the water. You seem to be equating a washing process with the process of microwaving kitchen sponges (and oh thank you, new sponges going on my shopping list now) to kill off the bacteria and godknowswhat living in them. I have always assumed that while some filters can be washed and reused (e.g. the metal filter screens in such things as dishwashers and certain kinds of extractor fans), some can't (e.g. the charcoal filters in other extractor fans).

Large supermarkets will sell their own-label brita-equivalent filters. They generally work just as well, while being cheaper. And you can get one today, and not have to drink hideous London water again, while working out whether or not to do anything more fancy (are you in a position to install one of those under-sink filters with its own tap?). And it'll be better for your kettle, too.
posted by Lebannen at 5:27 AM on June 24, 2011


Boiling the charcoal will not remove the compounds that have adsorbed to it.
posted by Green Eyed Monster at 6:32 AM on June 24, 2011


OTOH, the filters last much, much, much longer than Brita claims... naturally; their marketing people write the packaging instructions.

I use mine until the water slows to an unusable drip. Our water is sulfury and iron-y (ironic?); even at the drip... drip... stage, all traces of those minerals are removed.
posted by IAmBroom at 6:39 AM on June 24, 2011 [1 favorite]


The resin used for softening is probably the same stuff as used as the resin-bed in most household water softeners. This is probably why you can only find industrial quantities for sale.

These are cleaned of the accumulated minerals during the recharge process, where the resin-bed is flushed with a strong brine solution. You might be able to simulate this process on a small scale. Though, in the end, it's probably more effective to just install a home water softener (unless, of course, you're in an apartment.)
posted by Thorzdad at 7:07 AM on June 24, 2011


I agree with IAmBroom, I use my filters for like 8-10 months before I buy a new one. They still work until the water doesn't come through anymore.
posted by magnetsphere at 9:08 AM on June 24, 2011


OTOH, the filters last much, much, much longer than Brita claims... naturally; their marketing people write the packaging instructions.

Brita has you toss them after a certain time because of the chances of bacteria growing on the stuff the filter media has adsorbed.
posted by oneirodynia at 9:23 AM on June 24, 2011


Brita has you toss them after a certain time because of the chances of bacteria growing on the stuff the filter media has adsorbed.

This is the crucial point. Bacteria grows quite well these filters; Brita treats them to slow the process. It is a Really Bad Idea and a false economy to fool around with this.

[I recall Matt H making this point from personal experience during his lab days...]
posted by mojohand at 10:41 AM on June 24, 2011


Thank you so much for all the thoughtful and though-provoking answers.

Could you open up the filter and use the innards?
Well, yes, but that's still going to be massively expensive and a waste of plastic. And also less fun.

Boiling the charcoal will not remove the compounds that have adsorbed to it.
I think the main point of boiling the charcoal is to kill any kind of mildew, mould, bacteria or fungus that may decide to grow on there. This article actually seems to suggest that microwaving it could restore some of its adsorptive capacities, but it's a bit over my head and I think they microwave it for two hours or more. I would still be replacing the activated charcoal every couple of months.

These are cleaned of the accumulated minerals during the recharge process, where the resin-bed is flushed with a strong brine solution. You might be able to simulate this process on a small scale.
That's very interesting and indeed it would be incredible if I could re-use the exchange resin beads by using dishwasher salt or something.

it's probably more effective to just install a home water softener (unless, of course, you're in an apartment.)
I agree, but yes, I'm renting, and I'd like to be able to do this at work as well, where most of my tea consumption occurs. That gives me the idea that maybe I could find replacement exchange resin beads for home water softeners though.

It is a Really Bad Idea and a false economy to fool around with this.
Really? You might be right, but I would have hoped that regularly boiling the activated carbon would take care of that. Water filters aren't some sort of super-advanced technology.
posted by spaghettification at 1:10 PM on June 24, 2011


Regeneration of activated carbon is covered in the wikipedia article. Boiling is probably not going to do anything. Have fun with your project though!
posted by chairface at 4:22 PM on June 27, 2011


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