Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_28220 ( "Region" text, "Land area (km 2 )" text, "Rainfall by depth (mm/year)" real, "Rainfall by volume (km 3 /year)" text, "Surface run off (km 3 /year)" text, "Infiltration (km 3 /year)" text, "Evapotranspiration (km 3 /year)" text )

### Question ###
How many regions had rainfall infiltration (km 3/year) of 9.3?

### Accurate SQL ###

SELECT COUNT("Rainfall by depth (mm/year)") FROM table_28220 WHERE "Infiltration (km 3 /year)" = '9.3'