Baltimore’s public works department is expected to begin issuing water bills again this week, a spokesman for the mayor said, three months after the billing system was halted by a ransomware attack that crippled the city’s computer network.

The bills will be much larger than usual, covering service for at least May, June and July. Some customers might also be billed for April. For a typical household, that means a one-off bill of about $300 or $400.

The water department mailed postcards to its 400,000 or so customers in the city and Baltimore County last month telling them to expect the larger than normal bills soon.

Lester Davis, a spokesman for Democratic Mayor Bernard C. “Jack” Young, said more details about the bills will be shared Wednesday at the mayor’s weekly news conference.

Advocates for low-income water customers have warned that many households will struggle to pay the bigger-than-normal bills.

Officials have been urging customers to set money aside for the bills or mail in estimated payments. But they have also emphasized that payment plans, allowing customers to pay over six months or a year, will be available. Also, starting from May 6, the city will waive late fees.

While the Department of Public Works relies on revenue from its customers to fund its operations and building projects, Director Rudy Chow has said its finances remained healthy even while bills could not go out.

The ransomware hit May 7, bringing the city’s computers to a standstill.

Hackers locked city files and demanded payment, which the mayor refused to provide.

Since the attack, IT teams have been laboring to restore services. The water billing system is among the last used by the public to be brought back online.

Officials quickly developed a manual workaround to a problem blocking the Finance Department from issuing certificates showing outstanding debts against properties — a document necessary to complete the sale of a property. Employees’ emails were brought back online beginning at the end of May. The city’s ability to take electronic payments for fines and fees was restored in early July.

The city has projected that it will spend $10 million on the recovery and miss out on $8 million in revenue.

Officials have declined to say how the hackers penetrated the city’s network, but long before the attack they had received warnings that the city’s security systems were out of date and that infrastructure was vulnerable. The city’s IT department has also acknowledged that before the attack, it didn’t have a written plan in place to follow in the case of a serious incident, nor did it have insurance that has helped other jurisdictions pay for the costs of recovering.

Members of the City Council have expressed frustration with the city’s response to the attack and Democratic Council President Brandon Scott has established a cybersecurity committee to examine the hack and make recommendations to boost security.