Cliff notes, on the method:
In fact, an MIT team has discovered that this low-tech filtration system can produce up to four liters of drinking water a day — enough to quench the thirst of a typical person.
This experiment showed that sapwood is naturally able to filter out particles bigger than about 70 nanometers.
... was able to filter out more than 99 percent of E. coli from water.
I wonder how many limbs would be required for that 4L/day volume they describe. I mean, could a person simply cut 3-4 limbs and easily be able to keep a couple people well-watered all day?
Useful trick to know, either way. A liter here, a liter there ... and pretty soon you're talking about survival. Assuming there are such "dripping" trees around.