The only way to know for sure is to try

What I Learned Taking Apart A Pur Water Filter

Household appliances are not spared from the wrath of my curiosity

February 17, 2018

This week was the week where I decided NOT to write code during my free time. I spent most of it on sleep, some on gaming, some on drawing, and oh... taking apart a broken Pur Basic Faucet Filtration System out of curiosity.

It started when I bought and installed one. The questions I had were:

  • How is the indicator light powered?
  • How does it know water is passing through?
  • How does the electronics work when there's water involved?
  • How does it know the filter is already old?

When you search the internet for "How a Pur water filter works", most of the search results talk about the filter and not the faucet unit. So there's this gap in knowledge that I needed to fill. When our unit broke, I had no second thoughts taking it apart. And here's how it works:

[source] [green, yellow, red LEDs]
  |                 |
[Faucet]  [indicator electronics][reed switch] [filter insert magnet]
  |          [reed switch]                              |
[valve]---[magnetic water wheel]----------------------[filter]
  |                                                     |
  v                                                     v
[outlet]                                       [filtered water outlet]

The brains of the unit is the electronics. It is contained in a sealed compartment in the unit and is not connected directly to the parts that deal with water. In order to know what's happening outside the compartment, it makes use of magnets and reed switches. There's two magnet-switch pairs in the electronics:

  1. One determines if a filter cartridge is inserted.
  2. The other determines if water is flowing.

It all begins when you insert the filter which flips the first switch. Then it's the water flow from that point onwards, causing the second switch to flip whenever you use the filter. I have not torn down the electronics compartment and half of it is an opaque plastic, but I'm pretty sure there's a battery in there somewhere.


It's an amazing piece of engineering really, despite people calling out bad design and its tendency to crack open or burst at the seams. It's amazing how these small things make your house work, and not even give thought about the time and effort that went to designing these things. My hats off to the engineers for designing this fine product.