If you are on the market for underground water tanks, then you need to take the time to first determine exactly what you will be needing the tanks for. Will these be used for fresh drinkable water or will you be storing waste water in them? Are you planning on leaving them in the ground indefinitely, or have you contemplated moving them at a later date. These will be deciding factors with regards to your underground water tank selection. Another important factor will be the determination as to how much you plan on using or storing on a regular basis.