I think you have not laied DPC properly and use bricks which are manufactured with salty earth. Also you used the water having salt contents. For dampness and there removal you should visit the gharexpert.com website where you find lot of material about dampness. for ready refrence read the article link given below.
http://ww w.gharexpert.com/articles/Dampness-748/Which-various-types-dampness -in-building-their-treatment--0.aspx