The aim of the present study was to investigate the relationship between water, feed intake, relative body weight loss, and the weaning weight of piglets of lactating sows and to analyse the curves of water and feed intake. Data recording was performed on the Hohenschulen research farm of the Institute of Animal Breeding and Husbandry of the University of Kiel between April 2007 and June 2008. The sow herd had a size of 105 productive sows. The average water and feed intake, relative body weight loss of sows and the weaning weight of the piglets were 27.5 l day − 1 , 5.9 kg day − 1 , 0.5% and 8.7 kg, respectively. Average lactation length was 26 days. Water intake increased from day 1 to day 16 of lactation and remained constant until weaning. Second parity class sows had an increased water intake over the lactation period compared to younger and older sows. They also consumed more feed than older sows (6.1 kg day − 1 versus 5.7 kg day −1). The water-to-feed ratio decreased at the beginning until day eight of lactation. After a slight increase the water-to-feed ratio remained constant. The lactation period was divided into three stages (Stage 1: days 1 to 8 of lactation, Stage 2: days 9 to 16 and Stage 3: days 17 to 26). The correlation of water intake between adjacent stages was high 0.76 and 0.80. The relation of feed intake between Stages 1 and 2 and between Stages 1 and 3 was low. The correlation of the water and feed intake within the stages increased more than between these traits and different stages. But the negative values indicated that an increased water intake decreased the relative body weight loss. The relation between the second and third stages of feed intake of lactation and relative body weight loss showed that an increased feed intake decreased relative body weight simultaneously with an increase in the weaning weight of the piglets.