Water is a commonly spawned liquid in both Minecraft and Tekkit. It is very useful throughout the modpack in many different mods.
If you right-click on Water with an Empty Cell, the cell becomes a Water Cell, and the Water disappears. If you right-click on Water with a Bucket, the Bucket becomes a Water Bucket and the Water disappears.
If you put blocks of Water around your Nuclear Reactor, it will be cooled.Water can also be used in a Compressor to create Snowballs, these can further be compressed into Ice. This can be used as a cooling system in a reactor, but requires a lot of power.
A water source block doesn't have any EMC value, however a Water Bucket does. Therefore, the EMC of a water source block can be found by subtracting the EMC of a Bucket (768) from the EMC of a Water Bucket (769). This equals 1 EMC for each water source.
Water source blocks are handy because they can be stacked up to 64, while Water Buckets can only stack up to 1, allowing an easier way to move around water.