- after ingestion it is difficult to absorb water in the intestine, which is accompanied by an increase in the volume of its contents: the accumulation of water in the intestine and the dilution of the contents. Peristalsis increases and accelerates the emptying of feces. The effect usually occurs within 4 hours after ingestion. Unlike herbal laxatives, saline acts throughout the intestine. The rate of onset of defecation largely depends on the amount of water introduced with the salt. It is clear that with large amounts of water, laxative salt will act rather than with small.