heavy rainfall, runoff
潦 centers on water accumulating from heavy rain: the rainfall itself and the resulting runoff or flooding.
潦 combines 氵 (water) with 尞, which likely contributes the sound and relates to the idea of spreading or overflowing water.
Water 氵 plus 尞, which looks like a person under a roof with a fire, suggests water spreading like a flood after heavy rain.
For ロウ, imagine a row of houses getting flooded by heavy rainfall: row -> ロウ, and the water 氵 rises around them.
water damage; flood disaster