When I was building my home, I planned for my water tank under the kitchen counter in the corner of the "L". This is a space that is frequently difficult to access so why not put something in that space that does not need frequent access. One of the cheapest and strongest tanks I could find was a basic "spot sprayer" designed for garden use; mine is 26 gallons and approx. $60 with postage (from Northern Tool).
Below are a couple images showing the installation. The large diameter plastic hose is my water fill that hooks up to my exterior water fill panel.
The left hole is for filling the tank and the right side is for hooking up pressure water. The small round screen between the two fills is for venting the tank.
Let me know any questions and I will try to help with better information. (Purchase of any of these items through our links will give us a few pennies to cover internet costs and allow us to continue providing additional content, thank you).