the filtered water tastes weird, kinda plastic or chemical, even after running it for a week.

Diagnosis

The "plastic" or "chemical" taste in a new Aquasana AQ-5200 installation is typically caused by one of two things: carbon fines or volatile organic compounds (VOCs) leaching from the internal polyethylene (PE) tubing. New activated carbon blocks contain microscopic dust particles known as "fines." If the initial flush is insufficient, these fines linger in the filter housing and the delivery lines, imparting a bitter or metallic chemical taste to the water. Furthermore, the AQ-5200 utilizes high-density polyethylene tubing. When this tubing is first installed, the interior walls can harbor a residual manufacturing scent or "new pipe" taste. Because the filtered water moves slower through the narrow tubing than the main house line, these compounds can concentrate, especially if the system sat idle for a few hours during the installation process. If you have only been running the tap sporadically for a week, you haven't achieved the necessary flow volume to fully scrub the interior surfaces of the tubing and the depths of the carbon block.

How to Fix It

You need to perform a high-volume systemic purge to clear the carbon fines and strip the interior of the PE tubing. Follow these steps exactly:

1. Place a large 5-gallon bucket or basin under the filtered water faucet.
2. Turn the cold water supply valve to the fully open position.
3. Open the filtered water faucet and allow the water to run at maximum flow for a continuous 15 to 20 minutes. Do not turn the faucet off during this time; the goal is to create a constant high-velocity stream to push out trapped air pockets and carbon sediment.
4. If the taste persists after the 20-minute flush, you must isolate the tubing. Turn off the water supply.
5. Locate the connection point where the 1/4" polyethylene tubing meets the faucet assembly. Carefully depress the collet (the small ring) and pull the tubing out of the push-fit connector.
6. With the tubing disconnected from the faucet, open the water supply and run the water directly from the tubing into the bucket for an additional 5 minutes. This ensures that any contaminants trapped specifically in the faucet's internal mixing valve are bypassed and the tubing is fully scrubbed.
7. Reinsert the tubing firmly into the push-fit connector until it seats completely, then test for leaks.

If That Didn't Work

• Check for O-Ring Lubricant: Inspect the filter canisters. If a silicone-based lubricant was used excessively on the O-rings during installation, it can leach into the water stream. Remove the canisters, wipe the O-rings clean with a damp cloth (no soap), and re-seat them.
• Inspect the Cold Water Feed: Ensure the system is connected strictly to the cold water line. If the T-adapter was installed on a line that receives any backflow of warm water, the heat can cause the polyethylene tubing to release chemicals and odors more rapidly, leading to a persistent plastic taste.
• Verify Filter Orientation: Confirm that the filters are installed in the correct sequence and direction. If a filter is installed backward, the water may be channeling through the plastic casing rather than the carbon media, leading to poor filtration and a chemical taste from the housing itself.
• Check for "Dead Legs": If your tubing has excessive loops or "coils" stored under the sink, these create stagnant areas where water sits and absorbs the plastic taste. Trim any excess tubing to the shortest possible distance between the filter and the faucet.

Heads Up

• Never use hot water in the AQ-5200 system; high temperatures can damage the carbon block structure and cause the PE tubing to degrade or leach chemicals.
• When replacing filters in the future, always perform a 10-minute flush before drinking to clear out new carbon fines.
• Periodically check the push-fit connections for "creep," where the tubing slowly backs out of the connector, which can introduce air bubbles and affect taste.
• If you have an extremely high mineral content (hard water), the carbon may saturate faster; ensure you are using the correct filter replacement schedule to prevent "breakthrough," where trapped chemicals are released back into the water.