The discussions Wednesday at the Bend City Council meeting about water supply treatment made it sound like the city doesn’t know how much it can rely on its wells. As usual, the facts are more nuanced.

There’s no need to panic or spend hundreds of thousands on a new water system study, right now. But the concern has a way of giving more weight to the argument that the council should pick membrane filtration treatment over ultraviolet for Bridge Creek.

Bend gets about half its water from surface water — the Bridge Creek watershed — and half from wells. This dual source system is an advantage. If one supply is disrupted, the other can help compensate.

The disruption could happen for any number of reasons. A wildfire could endanger the watershed, in part by creating a flood of particles. Environmental regulations could change. Wells could fail or there could be a change in the aquifer.

The city already shuts down the water from Bridge Creek from time to time every year because of excessive particles in the water. The Bridge Creek supply is shut off for an average of 54 days in a year, usually in the early fall and in the spring. It has been shut down for as many as 100 days and as few as 20. So what’s the problem?

The shutdowns of Bridge Creek are a worry if the shutdown occurred for a sustained period during peak water usage in the summer, City Engineer Tom Hickmann told us. “We have never had to run it this way long enough to see how many days can we go before it creates very serious problems,” he wrote in an email.

One issue is that the city’s wells don’t feed into the city’s water in a way that allows the pumped water to be used anywhere in the system. So if some wells breakdown, it could create problems in some zones of the city.

Although the city may not know how long it can go on wells, it has made an effort to be prepared. The city has identified the system’s critical pipes. It has looked at the valves necessary to isolate any break. It has looked at how it can operate more efficiently.

On Tuesday, the Bend City Council is holding a special meeting on the related decision before it of what water treatment to use on Bridge Creek to meet federal requirements.

There are numerous benefits and risks to the alternatives. In short, ultraviolet is cheaper, maybe $28 million, instead of $36 million. Membrane does do a much better job, though, of keeping Bridge Creek water usable when particles are a problem. That helps more with a critical issue now and in case of a watershed fire.