Percolate comes from a Latin verb meaning "to put through a sieve". Something that percolates filters through something else, just as small particles pass through a sieve. Water is drawn downward through the soil, and this percolation usually cleans the water. A slow rain is ideal for percolating into the soil, since in a violent rainstorm most of it quickly runs off. For this reason, drip irrigation is the most effective and water-conserving form of irrigation. Percolation isn't always a physical process; awareness of an issue may percolate slowly into the minds of the public, just as Spanish words may gradually percolate into English, often starting in the Southwest.