Table 1. Definitions and nominal values of parameters used in the model.

Parameter	Equation	Nominal value
Pressure gradient between arterial and venous PVS		226 Pa
Capillary basement membrane resistance for half the length of one AU
ECS resistance for half the length of one AU
IEG resistance for the thickness of an endfoot
Resistance of intracellular pathway in the astrocyte processes for half the length of one AU
Endfoot membrane resistance
Resistance of the plasma membrane in half of the astrocyte unit
Gap junction resistance

Derivations are documented in Supplementary Information S1. Total flow resistance in the ISF space between arterial and venous PVS; Nominal Interstitial fluid flow rate; Resistance of a single ECS pathway for half the length of one AU; D_AU Diameter of the astrocyte unit; n_capillary Average number of capillaries in one AU; K_BM hydraulic permeability of the capillary basement membrane; A_BM the cross section area of basement membrane; n_ECS Number of parallel ECS pathways in one AU; μ dynamic viscosity of ISF; T_EF endfoot thickness; L_EF endfoot length; H_IEG thickness of IEG; τ_PR Tortuosity of the astrocyte processes; D_PR Diameter of astrocyte process; C_AQP4 Water conductivity of a single AQP4; S_EF and S_PM Endfoot and plasma membrane surface areas, respectively; and AQP4 densities over the endfoot and plasma membrane, respectively; Water resistance of single gap junction channel; d_GJ density of gap junction channels; S_GJ surface area of the contact region between neighbouring astrocytes.