Low Efficiency and Water

I live in Dallas and we have somewhat alkaline water. Yesterday brewed Biermunchers Centennial Blond and got 57% efficiency rather than 68-72% typical for me.

Everything was same including the crush but used 2 gallons distilled water in addition to 2 gallons of tap for the mash. My idea was to dilute the alkalinity since this beer is lighter SRM

I am guessing ph was wrong due to not enough acidity from malt. Any thoughts?

I agree that your water was off due to the lack of malt acidity. Ususally if I do a lighter beer, I'll just throw some PH5.2 buffer in there. On all my other beers, I usually get around 75 to 80%.