关于twice as many/much as结构:
(1) If you say "twice as many", then this construction should be paired with acountable noun. e.g., twice as many dogs --> "dogs" is a countable noun
(2) If you said "twice as much", then this construction should be paired with anuncountable noun. e.g., twice as much water --> "water" is an uncountable noun
(3) If the noun in question is already an explicitly numerical quantity, then you should use neither "much" nor "many". Instead, you should just use "twice" or "double" by itself. e.g., twice the increase --> "increase" is an explicitly numerical quantity
(4) These rules are followed pretty closely. so, for instance: twice as much water --> correct, since "water" is an uncountable noun (but is not an explicitly numerical quantity) twice the water... --> incorrect, since water is not a numerical quantity twice as much as the increase... --> incorrect; redundant twice the increase... --> correct