John has a very inefficient toilet that uses 5 gallons of water per flush and his household flushed 15 times per day.  He replaced it with a toilet that uses 80% less water per flush.  How much water did John save in June?
He used to use 5*15=<<5*15=75>>75 gallons of water per day.
This means he used 75*30=<<75*30=2250>>2250 gallons a month.
His new toilet uses 5*.8=<<5*.8=4>>4 gallons less water per flush.
So, it only uses 5-4=<<5-4=1>>1 gallon per flush.
That means he uses 1*15=<<1*15=15>>15 gallons per day.
All in all, it accounts for a total usage of 15*30=<<15*30=450>>450 gallons.
So, he saved 2250-450=<<2250-450=1800>>1800 gallons per month.
#### 1800