Answer: In scientific notation = 8.12\times10^5 gallons of water in an olympic training center's pool.
Explanation:
Given: 812,000 gallons of water in an olympic training center's pool.
In scientific notation ,

Scientific notation is a way to write a very large or a very small number in the product of a decimal form of number [generally between 1 and 10]and powers of ten.
Therefore,In scientific notation = 8.12\times10^5 gallons of water in an olympic training center's pool.