Simply put... can i use spring water for my tank. i don't care about the expense?

i just bought a new 2 gallon tank. I'm a beginner and i know its not the best size for me. when i first got the tank i put in these tap water conditioner drops. the pet store worker said it was to get rid of the chlorine. My tank has been running for about a week. They pet store workers said i could then put fish in. i bought one glofish, one tetra, and one guppy. As of now i only have the glofish. they others just died. Im wondering if i could just start over with spring water and maybe a few chemicals and i can finally have some fish. i have been at this for a while and have lost a couple more fish due to the water. so please give me a straight answer someone and just tell me if i can do it. i dnt care about the cost of the spring water.