I was just walking past our new in-ground rain barrel. It's actually a steep sided pond
with a pvc liner but its main purpose is to collect run-off so we can water
a nearby planting area. The soil is quite sandy and we covered the edge of the liner with sandy loam (our topsoil). I noticed one stretch of the pond berm
was moist and growies were growing. It hasn't rained for 4 days. The nearby stretches of the pond edge were dry and the growies were still growing but I doubt they are as happy. The difference is that on the moist section, the soil on top of the pond liner is touching the water and wicking the water up to a foot through the soil. The rest of the pond berm has a wrinkle or is too vertical to hold soil.
So I learned that if I have my soil touching water, it can wick it up to a foot away.
The red dots indicate the far edge of the wicked moisture.