I use pure spring water from Polaris that I buy at Costco at $6 for a 5gl jug. Before that I used spring water from a local artassian well, however as everyone under the sun was starting to use this water which in return caused many traffic accidents-so it's now closed
For the past 5+ years I have used local and bottled spring water and have never had any problems with algae and such. My tank is only a 27gl so I don't mind picking up at bottle once a month, and toping off with a 500ml once a week
cheers, Rich