The city of San Diego sent her a $740 water bill in August. And two months later - she got another for $954.
But the water meter outside her home is stuck at zero.
"When it is evident that the meter is not working, then don’t send me a bill for $954 when I’m generally paying $350," said Hernstad, who lives in La Jolla.
Hernstad's story is one of many coming to light as the city auditor's office expands its probe into how the water department operates.
For months, San Diegans have complained of stunningly high water bills, with no apparent help from the city to solve the problem. Many said they were told they either had a leak, or that their meter was new and more accurate.
But last week, the city admitted that about 300 customers in four neighborhoods were overcharged by an average $300 for human error reading older meters. The city is now examining all 250,000-plus meters across San Diego.
On top of that, city auditor Eduardo Luna and his staff of 20 are expanding their investigation to look into how water bills get to a customer's door.
"Some of it is in house, some of it is behind a computer screen, other times it is actually verifying and talking to various personnel, reviewing accuracy of water bills, sometimes it's ride-a-longs," Luna said. "It's going to vary."
Hernstad's problems stemmed from an August 2016 issue with her irrigation system. It caused her water bills to rise from the typical $350 every two months to more than $700.
Hernstad paid the higher bills, fixed the system, and her water bills went back to normal.
But sometime after that her meter stopped at zero.
Then, in August 2017, she got the $740 bill, followed by $954. She called the city, and found out that she was billed based on her prior year's activity in the same time period. In other words, exactly one year ago she had the irrigation issue, and that's why her bill went up.
Hernstad says she called the city and visited in person, only for her complaints to fall on deaf ears. She wants the city to instead bill her based on her normal average, not a one-off for an issue she fixed.
"It actually makes you feel, as a consumer, that you don’t have a leg to stand on, and that’s not what we pay taxes for," she said.
Hernstad paid the bills because she was threatened with a shut-off notice.
The city says during the probe it will not turn off anyone's water if they are disputing a bill. 10News inquired about Hernstad's situation, but a city spokesman did not immediately provide a response