Just a nit to be picked or a curiosity for those who may be interested, the water filters are often chemical, not physical, ones. A “physical” filter acts like a sieve, it’s got holes where the removed stuff gets stuck simply because of size (active carbon and diatomaceous earths are the most extreme examples of this); a “chemical” filter, such as a water ion-exchange purification system, contains an inert polymeric core with lots of reactive branches, and the ends of these branches get exchanged chemically with the items that need to be removed.
In the case of a water ion-exchange purification system, there is a part of the system which removes negative ions (such as Cl-) and provides hydroxils (OH-), another which removes positive ions (Na+, Ca[sub]2[/sub]+, Mg[sub]2[/sub]+).
Exchange columns are used in many other applications, mentioning just two for info’s sake:
- removing lactose from lactose-free milk (depending on the location, the end result has legally to be called “lactose-free dairy product”) in a way that doesn’t leave the milk tasting sweeter than regular milk (adding lactase to break up the lactose without removing it, while perfectly fine from a health point of view, breaks the lactose into two smaller, sweeter-tasting sugars… this leads to consumer rejection)
- synthesizing (small) proteins, which IIRC correctly was the original use of this kind of system
A carbon active or DE filter can remove tiny particles, but not salts.
And just as anecdata, the “distilled water” which was so popular for carwashing in several of the factories where I’ve worked went through DE or carbon / ion exchange / DE or carbon, to remove: particulates, salts, any possible particulates broken off from the ion exchange.