Answers · The supply line and the filter
Copper or Braided Steel for the Supply Line?
The short answer
Either works on ordinary tap water, since Sub-Zero's Designer, PRO and UC-15I guides accept 1/4-inch OD copper, braided stainless steel or PEX, but behind reverse osmosis the line should not be copper.
Check in this order
- Look where the line leaves its shut-off valve, and note whether it is copper, braided or plastic.
- Follow the visible run for kinks or flattened bends, and feel each reachable fitting for damp.
- Stop using blue or green ice, which Sub-Zero traces to copper corroding in the line.
- Have a plumber replace a copper line that runs after a reverse-osmosis unit.
Past this line it is a technician's job Sub-Zero Repair Tacoma, (206) 472-1140
Behind the answer
Those installation guides also ask for about three feet of spare line at the connection, and they rule out self-piercing valves.
Reverse osmosis is the firm rule: Sub-Zero says copper after the system can leach. Whatever the material, the PRO and Designer guides say the line must never be exposed to freezing temperatures, which matters in an unheated crawl space.
Related questions
Who replaces the water line to a Sub-Zero?
A plumber, from the shut-off valve to the wall. The stretch under the unit sits behind the kickplate and is technician work, as is anything inside the cabinet. If the ice misbehaves after a new line goes in, call Sub-Zero Repair Tacoma on (206) 472-1140 before anyone moves the unit.
- Signed
- Marta Fennimore
- Role
- Refrigeration technician — ice systems and water supply
- In the trade
- 12 years
- Holds
- EPA 608 certified
- Checked
- Sep 18, 2026