Will a regular sait water enema relieve stool impaction in rectum?

Depends, maybe. Depending upon the extent of impaction and the hardness and density of the stool, salt water or mineral water enemas may help (the latter is more comfortable due to lubrication of the anal canal). If these strategies along with laxatives fail, you need an evaluation by an ER doctor or a gastrointerologist to assess for location of the impaction to develop a reasonable treatment plan.