Hi
I'm new here but, here are some clips from the Washington State Medical Marijuana Act
This is the states definition, so I guess you just do what they say.
I'm not sure if countys have any say on this, but You can read the full text at this link.
I692-Full Text

RCW 69.51A.010 Definitions

(2) "Primary Caregiver" means a person who:
(a) Is eighteen years of age or older;
(b) Is responsible for the housing, health, or care of the patient;
(c) Has been designated in writing by the patient to preform
the duties of primary cargiver under this chapter.

RCW 69.51A.040 Qualifying patients' affermative defense

(4) The designated primary caregiver shall:
(a) Meet all criteria for status as a primary caregiver to a
qualifying patient;
(b) Possess, in combination with and as an agent for the
qualifying patient, no more marijuana than is necessary
for the patient??s personal, medical use, not exceeding the
amount necessary for a sixty-day supply;
(c) Present a copy of the qualifying patient??s valid
documentation required by this chapter, as well as
evidence of designation to act as primary caregiver by
the patient, to any law enforcement official requesting
such information;
(d) Be prohibited from consuming marijuana obtained
for the personal, medical use of the patient for whom the
individual is acting as primary caregiver; and
(e) Be the primary caregiver to only one patient at any
one time.[1999 c 2 ? 5 (Initiative Measure No. 692,
approved November 3, 1998).]