Pilot flying M20K aircraft reported pitot static system malfunction inflight.

Narrative

Unreliable indication of airspeed; vertical speed and altimeter in IMC with moderate turbulence. Blind encoder also is fed from same pitot/static system and considered unreliable. The pitot static system ingested water and appeared to have been unable to drain water from moderate rain encountered. Pitot heat was on prior to IMC; once Visual flight conditions were reestablished; Pitot heat was cycled; getting a positive response from the ammeter. Airspeed varied slightly by application and removal of pitot heat but remained very low throughout. Airspeed/VSI/Altimeter were considered unreliable for the rest of the flight. Aircraft was inspected on the ground by PIC and line attendant. Both Pitot and static lines have manual drains; both were opened and no water noted. The pitot tube and drain were verified open; and the next day probed to confirm unobstructed. Nothing was found. In addition; both static ports were inspected along with accessible portions of the static system tubing (relatively clear tubing); nothing was found. Pitot heat was verified by feel; sat. Water did drain from the aircraft upon landing and may have been clearing the system normally. The aircraft was flown the next day with normal airspeed; VSI and altitude readings. The pitot static system was verified a few days later with no leaks and in cal. Aircraft is due for its annual within the next month; I have squawked the pitot/static system specifically the drains with the intent of finding a deficient condition. Until then the aircraft will not be flown IMC; nor into any precipitation.