Forrest is playing with figures in a silly attempt to minimize the extent of the drawdown. 

Forrest had to resort to silliness in an attempt to mislead people. 

Here is what Forrest said (emphasis supplied):

"...the average drawdown today is only about two feet a year over the life of the wells, compared with about a foot a year five years ago."

Imagine man who had a leech attached to his body 10 years ago and has lead an active life over that time.  However, in the last few days, his body has been covered with leeches. 

Imagine that in the few days that his body has been covered with leeches, the critters have sucked around 3 quarts of this guy's blood out of his body. 

Since the human body only contains about 6 quarts of blood, the last few days of this guys' life haven't been real rosy.  In fact, this guy is in very dire straits (the leeches are in a little bit of trouble themselves as they're about to run out of blood).

However, Forrest would tell the guy not to worry because, ". . . the average blood loss today is only about 0.3 quarts of blood per year over the time since the first leech was attached 10 years ago."

Unfortunately, since the guy has lost a whole lot of blood in the last few days, he probably wouldn't be able to hear Forrest's reassuring words.  If he can hear at all, with the lack of blood flowing to his brain, the guy might actually believe Forrest.

One wonders why Forrest compelled to try and mislead folks with this sort of silliness.

Also recall that when Forrest was asked if the plunging water table was a crises, he said "absolutely not."

Readers listening to Forrest can make up their own minds whether he can be believed or not.