Just my opinions...
1. Looking for the best water in LA is kinda like looking for the best smelling fart. Our tap water is pretty hard so I almost always cut it with some RO water from a dispenser and add lactic acid and CaSO4 and/or CaCl2. And the tap water in Glendale is treated with chloramines so I also hit it with some potassium metabisulfite (which I always have around for wine making). For something like a pale ale, I might use 50% RO. I might use more for a lighter style and less for a darker style.
2. I'd probably try the shop in Woodland Hills for keg stuff, or make a road trip to MoreBeer in Riverside.
3. On your way there, stop at Star Restaurant Equipment on Sepulveda in Van Nuys for spoons and strainers.