So I only need to run one GEC even though each unit's water pipe is directly fed from the street?
Yes, only One GEC is needed to Bond the Service Equipment to the Cold Water Grounding Electrode.
At least (1) additional Electrode will be required to supplement the Cold Water Electrode.
if so, there would be ungrounded water meters in 3 of the four units.
We are using the Cold Water line(s) as an Electrode, which in itself is a Grounded entity.
The City Cold Water piping _SHOULD_ be commonly connected on the "Street" side of the Water Meters.
Each unit has its own water meter and copper pipe feed from the street in its own basement.
Your AHJ might request that you to Bond all of the Cold Water lines together via a Copper Conductor, so as to create a Single Electrode.
This may be accomplished in several ways;
a. Bonding all Water Pipes together, using a Single Conductor,
b. Jumpers around all Water Meters,
c. Bond each Tenant's Cold Water line to the EGC from each Panelboard Feeder,
d. Reference Article 250 for other approved Bonding methods.