1) rock formation properties and the level of the completeness
While drilling into hard and fine – grained formations with low rotary speed and few cuttings of small grain size. The flushing water could be less; in soft, medium hard and coarse-grained formations with high rotary speed the flushing water should be increased to discharge the debris effectively

2) bit type
High rotary speed is usually used on impregnated core bit, because of the fine diamond grains on impregnated core bits, more flushing water should be used to cool the diamond grains and the matrix of impregnated core bit, so as to avoid the diamonds damaged from oxidation and graphitization, and pretect the bit matrix from being worn too fast by the debris. The self-sharpening ability of surface set core bits is better than that of impregnated core bits, also, surface set core bits have advantages on debris removal and cooling, so its flushing water can be a little less than that of impregnated core bit

3) besides, the performance of the bit matrix, diamond size, bit waterways, rotary speed, drilling pressure also affect the flushing water. Those all be taken into consideration