(1) The principle of dry ice precipitation enhancement is: dry ice absorbs a lot of heat when sublimating, which makes the water vapor in the cloud condense into small raindrops, so the answer is: dry ice;

(2) More calcium and magnesium ions in hard water will affect the foaming of soap, so soapy water can be used to test whether water is hard water or soft water, so the answer is: soapy water;

(3) Activated carbon can adsorb pigments and odors in water, so the answer is: adsorb pigments and odors in water;

(4) Heating and boiling can not only reduce the hardness of water, but also sterilize it, so the answer is: heating and boiling.