Carbon dust from a new filter. Normal. Not harmful, but unpleasant.
Flush the filter. Run cold tap water through it for 15 seconds before first use. Install it. Discard the first three full pitchers of filtered water. Do not drink this water. Use it for plants.
If taste persists after three pitchers, check insertion. Filter groove must align with reservoir ridge. Press firmly for a tight seal. Loose filter can cause poor contact and off-taste.
Use only cold tap water. Max temperature is 85°F (29°C). Hot water damages the filter media.