Los Angeles/Orange County resident here. Why does San Francisco’s water taste different?

I recently visited, and no matter where I went: public drinking fountain, fast food, upscale restaurant; all those places had water that tasted exactly the same, but most different from what water tastes like in LA or Orange County. Why is that?

I’ve previously visited London and Japan, and the water did not taste different like what I experienced in San Francisco. Any ideas?

Edit: I’ve learned a ton from you guys here! Many thanks! Wonderful info!