The Pentair 161110 GRO-350B is a 3-stage reverse osmosis system that connects to your cold water supply line, a dedicated drinking water faucet with air gap, a drain connection, and its own 2.1-gallon storage tank. It reduces lead, TDS, arsenic, nitrates, and chlorine taste and odor, and is Pentair's most compact RO system.
Before You Begin
- Tools needed: a hand or electric drill (cordless preferred), two adjustable wrenches, slotted and Phillips screwdrivers, a file, safety glasses, drill bits (1/8", 3/16", 1/4", 3/8"), a tube cutter or utility knife, a pencil, a towel, and a bucket. If your sink doesn't have a hole for a separate faucet, add a center punch, a 3/4" hole saw or drill bit, and a safety mask.
- Safety first: Install on the cold water line only. Your water supply should be within 50–100 psi (note: this system needs higher minimum pressure than Pentair's other RO systems), 40–100°F, under 2000 ppm TDS, under 10 gpg hardness, and pH 3–11. Do not use with water that is microbiologically unsafe or of unknown quality without adequate disinfection.
- Cartridges: The GRO-350B uses FDF1-RC, GRO50-RC, and F1GC-RC cartridges, which come pre-installed in the correct sequence.
Step-by-Step Installation Guide
- Turn off the cold water supply line (install a shut-off valve first if needed), drain the line, then install the feed adapter valve onto the supply valve and connect the riser to it.
- Choose a faucet location and drill a 3/4" hole if needed. Mount the faucet with its drain tubing, chrome plate, and locking nut — making sure the 1/4" red RO drain line (with its flow restrictor still attached) is securely connected to the system manifold before attaching it to the faucet.
- Connect the 1/4" drain line from the system to an appropriate drain connection per local plumbing codes, then run a straight, kink-free path from the faucet's 3/8" drain tubing to the drain clamp to prevent reject water from leaking through the air gap.
- Mount the system vertically in a solid location under the sink, then connect the blue outlet tubing from the faucet to the system.
- Connect the storage tank to the system: wrap the tank threads with plumber's tape, thread on the tank valve, then run blue tubing from the tank valve to the system's quick-connect fitting. Mount the system on the wall and connect the remaining blue tubing from the system to the water supply adapter.
- Close the tank valve, turn on the cold water supply, and lift the faucet handle to lock it open, letting it drip for 30 minutes, then fully open the supply and let it drip for 12 more hours. Close the faucet, open the tank valve to fill (about 3 hours), then flush the post-filter by opening the faucet for 4–5 minutes and letting the tank refill — repeat this fill-and-flush cycle 4 times, checking for leaks throughout.
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