Playing with the water transparency revealed a bug in the CPU rendering of surfaces inside transparent materials.
Fixed in #Avoyd beta 0.21.0.871 https://www.enkisoftware.com/products
Thanks everyone for your feedback. Most answers congregated around an Absorption Length = 8 so we'll change the default Minecraft water and flowing_water to that in the next full release of Avoyd.
Took a break from improvements to the GPU path tracer to test making a stylized volcanic eruption using the Minecraft map the Continent of Lisrina by Dannypan.