Our communities deserve cleaner water. But who will pay the billion-dollar climate bill?

Jake Wilson is the mayor of Somerville.

The Mystic River is just a short walk from my home, but its peaceful waters belie a disgusting reality: During heavy rainfall, a mixture of sewage and stormwater is discharged into the river. It’s called a combined sewer overflow, and it happens far too often.

Fortunately, we’ve been working as a region since the 1980s to fix this through building and upgrading infrastructure and treatment plants. Though the costs are high, there’s no question that the work is essential. Just as important, we need to figure out as a Commonwealth how we will fund this in a way that does not place the highest burden on ratepayers most unable to carry it.

Somerville and Cambridge, along with our partners at the Massachusetts Water Resources Authority, recently submitted a Draft Updated CSO Control Plan to state and federal regulators. This plan is a legal requirement. It is also a moral imperative. The plan is the first in the nation to account for the effects of climate change, which has increased storm intensity. It recommends a series of projects that would eliminate CSOs in a 2050 typical year projected to have heavier rainfall more often than today. It is an essential step forward. However, it is a step that comes with a $1.29 billion price tag.

That cost is borne by water and sewer ratepayers in the communities the MWRA serves.

Somerville is a mixed-income community — many residents are already at risk of displacement due to high housing costs. Our water and sewer rates are among the highest in the MWRA system. To responsibly fund our share of this work, we will need to roughly double our water and sewer rates over the next four years to build the necessary reserves. Over time, the charges to our ratepayers will continue to increase far more than other MWRA communities paying a smaller share across the region.

It’s difficult to overstate what this extra cost, approximately $250 for an average household between this year and next, will mean to a low-income or even middle-income family in an area where the cost of living is among the highest in the nation. We’re not talking about people having to give up trips to coffee shops; people are already choosing between a full grocery cart and prescriptions; rent and doctor’s visits; tuition and dropping out.

Still, there are many advocacy organizations and individuals who are urging us to go further and do more — including a plan that would fully separate sewers systemwide, driving the cost up to roughly $4 billion while still not fully eliminating discharges. I agree that there is more work to be done. Making additional, meaningful progress, however, will require a regional approach that extends beyond our municipal borders and investment beyond what households can absorb in their water and sewer bills.

If our communities are going to be truly livable in 2050, we’re going to need to make major progress toward addressing the impacts of climate change and the ever-rising cost of living. The work to address CSOs brings the critical link between these two crises into sharp relief.

Climate change is expected to overwhelm existing sewer and drainage infrastructure in communities across the state — resulting in local flooding, serious health risks, and water pollution equal to or worse than CSOs. The years of intensive study and modeling of climate change conditions that went into this plan have only reaffirmed this fact and increased our understanding of the challenges ahead.

Communities like Somerville across the Commonwealth — Lowell, Lawrence, Springfield, New Bedford and other cities and towns full of hard-working people struggling to afford the essentials — will all need to overhaul their systems and should not be left to tackle this alone.

To prepare for a resilient climate future, taxpayers need regional and state-level solutions. More state-level investment is needed. We need to think creatively. Subsidized or zero-interest loans, establishing a state fund for mitigation work, rate-payer assistance programs that currently are not legal in Massachusetts, everything should be on the table.

The challenges today are beyond what we faced in the 1980s when the region first took this on, and our solutions need to evolve to the changing climate that is here and ahead.