The program has been going on for decades. The Feds put money in a big account the EPA manages that gives grants and loans to areas that need it to get the process completed faster.
As loans get repaid over the years, the money is leant out again. Most areas have enough income to afford the project, but not enough cash on hand to afford to pay all at once.

This is the first batch of additional money being added to the fund along with a mandate that the problem be resolved in a fixed timeframe.

Currently the fund has used about $20billion to provide $40billion in upgrades over nearly 30 years.

https://www.epa.gov/newsreleases/biden-harris-administration-issues-final-rule-requiring-replacement-lead-pipes-within

Funding: The Bipartisan Infrastructure Law provides $50 billion to support upgrades to the nation’s drinking water and wastewater infrastructure. This includes $15 billion over five years dedicated to lead service line replacement and $11.7 billion of general Drinking Water State Revolving Funds that can also be used for lead service line replacement. There are a number of additional pathways for systems to receive financial support for lead service line replacement. These include billions available as low- to no-cost financing through annual funding provided through the Drinking Water State Revolving Fund (DWSRF) program and low-cost financing from the Water Infrastructure Finance and Innovation Act (WIFIA) program. Funding may also be available from other federal agencies, state, and local governments. These efforts also advance the Biden-Harris Administration’s Justice40 Initiative, which sets the goal that 40% of the overall benefits of certain Federal investments flow to disadvantaged communities that are marginalized by underinvestment and overburdened by pollution.