Water filters for the Bidet Toilet Seat are not required but Bidet Manufactures recommend using either an Ion or Sediment water filter for your Bidet Toilet Seat to help keep your Bidet in good working order.
The Ion water filter was designed to reduce the surface tension of the water and keep calcium (hard water) from building-up and to keep small particles (particulates) out of the water supply of your Bidet Seat. If you don't have hard water, then I would suggest the Sediment water filter.
Suggested Replacement for water filters are from 6 to 9 months depending on water condition. If you have exceptional water quality or a whole house water filter, then a water filter for your Bidet Toilet Seat won't be necessary.
When you choose 3 Ion Water Filters the cost is $53.95, giving you a savings of $20.90 over buying just one and no extra shipping charge.
This image is an example of how the Water Filter can be connected to your Bidet Toilet Seat and they can also be connected at the T-connector.