how many inches of rain did hurricane allison bring to houston
Over 40 inches.
Tropical Storm Allison
The storm dropped heavy rainfall along its path, peaking at over 40 inches (1,000 mm) in Texas. 
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Tropical Storm Allison [SEP] Introduction
Following the storm, President George W. Bush designated 75 counties along Allison's path as disaster areas, which enabled the citizens affected to apply for aid. Then the fourth-costliest Atlantic tropical cyclone and still the costliest Atlantic tropical cyclone that was never a major hurricane, Allison was the first Atlantic tropical storm to have its name retired without ever having reached hurricane strength.