The Water Tank is a RailCraft device that provide a source of Water to the Railway system. Another operation that is made up of more than one block, it is made up of 26 Water Tank Siding blocks (aka Banded Planks). It is built as a 3X3 square on the ground, then another on that just without the middle, then another 3X3 square on top of that which should make a 3X3X3 cube without the middle (similar to the Coke Oven).
After the Tank is created, right-click to generate Water at about 40 units per 15 seconds.
The Water Tank can hold 400000 units of Water and a Bucket holds 1000.
In about 41 hours the whole Water Tank will fill up which is equal to 400 Water Buckets.