**3. Dairy water quality and milk production**

The quality of drinking water is often one of the causes limiting its intake. Water quality is measured in chemical, bacteriological and physical terms, through laboratory tests. To avoid significant production losses each of these aspects must be carefully and regularly evaluated.

Regarding chemical composition, the concentration of total dissolved solids (TDS) and the prevalent salts represent the quality factors that can seriously limit milk production in many regions. There is controversy regarding the maximum levels of salts that affect the performance of dairy cows. Water with TDS> 7000 mg/L would not be suitable for high producing cows (>35 L/day), but would have little effect on low-producing animals (<25 L/ day) (Bahman et al. 1993; NRC, 2001). Experiments conducted in Israel (Solomon et al., 1995) showed that water with TDS above 4000 mg/l produced negative effects on cows producing an average 35 l/day, when temperature was above 30°C.

All sulfate salts (Ca2+, Na+, Mg2+), when exceeding 1500 mg/L, can decrease productivity because of their laxative effect, the most potent being sodium sulfate (Socha et al., 2003). However, livestock drinking water high in sulfates (1000 to 2500 mg/L) initially suffer diarrhea, but then a process of habituation begins. Moreover, ingestion of "light" water, i.e. very low in TDS, is also considered detrimental to productivity, especially when levels of sodium chloride are very low.

The temperature of drinking water could be another factor limiting intake. For example, in an experiment conducted in Texas (Wilks et al., 1990) it was observed that cows drinking water cooled to 10°C presented lower respiration rate (70 VS. 81 rpm), lower rectal temperature in the afternoon (39.8 vs. 40.2°C) and higher milk production (26.0 vs. 24.7 L/ cow/day), as compared to animals drinking water at 27°C.
