5

The water inlets to each of the four barrels is connected to a 5 gallon bucket that distributes water to these inlet pipes. I cut a 4" pipe length-wise along the drip line of the house to divert water into this bucket:
















Next, I added smaller gravel to make a smoother surface:
Also, I cut some 4" pipe length-wise to act as a gutter to funnel water into the bucket.