1. Introduction
Water is often referred to as ‘‘the forgotten nutrient’’,
and it has received less attention than any other nutrient
(Brooks and Carpenter, 1990). That is why the water
requirements of pigs are not as well understood as those
for other nutrients. There are two main reasons why it is
difficult to establish water requirements: first of all, water
needs can vary considerably depending on the animal’s
physiological state, rearing environment and diet. Secondly, a consumption-based approach to the water
requirements of pigs may not be accurate due to inevitable waste. The EFSA (2007)opinion on the welfare of
fattening pig states that the availability of fresh drinking
water is important, particularly for dry-fed pigs. It has
been extensively confirmed that water intake influences
dry matter intake and therefore pig growth performance,
and that the welfare of pigs is compromised if water is
unavailable (Kyriazakis and Savory, 1997). According to
EC legislation (Council Directive, 2008/120), all pigs over