Lets say your total weight of the stand and all the water is 10000lb. Each footing will need to withstand 2500lb. Dividing 2500lb by 128 (8x16) sq inches is 19.5 lb per sq inch. Lets take the same 2x8x16" footing and has 2x4 wood standing on it as the leg of the stand, then the 2" cinder block will need to have a compressive strength of over 381 lb per sq inch rating (2500lb divides by the area of which the stand is sitting on the block 1.75"x 3.75").