For many reasons, especially in a hydroponic setting, water is what drives the plant transpiration cycle. Without water, plants would not be able to uptake nutrients or transport nutrients within their tissue. 

Water is a carrier and transporter of nutrients to your plants and within your plants. While water facilitates many plant growth processes, and even though many of these processes cannot take place without the presence of water, most of the water itself reacts very little with the nutrient molecules in it.  Of course, that is only true if you are using distilled water or water that has been passed through a reverse osmosis filter. 

While water itself will not cause nutrient uptake problems, the dissolved salts and minerals also present in your water will.  Distilled and reverse osmosis water should show a TDS of zero ppm. As this number increases, the possibility of a nutrient uptake problem also increases. 

Most of the dissolved solids in water come from calcium carbonate. This and sodium can cause problems for your growing operation.  You need to fully analyze and scrutinize all elements in your water to provide supplementation to hit your nutrient, EC and pH targets in order to maximize plant growth.