Any way you look at it, blood is a precious commodity. Potable water is precious. For every human on the planet, there are about 88 million gallons of fresh, available water — though much of that is wasted or used industrially. By contrast, adults have roughly 1.35 gallons of blood (children start with less, but by age 6 have as much as an adult).

Consider, too, that the loss of 30 percent of your blood means the start of serious hemorrhagic shock, affecting the brain and blood pressure. At 40 percent, it can be fatal.

Now consider that blood isn’t completely transferable. It comes in a variety of types and Rh values that limit whether blood from one person can help another in need. And, many people can’t donate blood because of their size, age, health or other risk factors. So the supply of blood for those who need it — in fact, can’t live without it — makes it precious indeed.

Every day in America, on average, 36,000 units of red blood cells, 7,000 units of platelets and 10,000 units of plasma are needed. Typically, hospitals need about a five-day supply on hand.

The American Red Cross handles about 40 percent of the blood supply in the United States and is the most visible option in this area for donating (some area hospitals also accept blood donations). Working with local organizations and businesses, the Red Cross holds several blood drives every month.

But high school and college drives account for a good portion of that supply, and at the end of the school year, those sources, well, dry up.

We wrote, in January, that the supply was down to three days’ worth nationally — considered a critical shortage by the American Red Cross. Now, there’s less than a two-day supply of blood available for emergency rooms, where it can be most critical.

A general shortage when students go on break is normal, according to Mary Brant, external communications manager for the Red Cross of Northern New England. But inexplicably, the current shortage has particularly affected the supply of type O blood.

That’s especially problematic because type O is the most widely used blood type. Type O-positive blood is the most common in the U.S.; 37 percent of adults have it. And type O-negative blood — the “universal” blood type — can be given to anyone in need.

Between them, they account for 44 percent of Americans’ blood. But — again, for unknown reasons — this area has a particularly high concentration of type O donors. Thomas Hinman, who coordinates the Red Cross’s blood drives for the Northern New England area, reports donations in the Monadnock Region regularly include about 60 percent type O.

That means local donors have an outsized opportunity to help. Fortunately, such opportunities are available often. A few coming up were noted in a Sentinel report this past weekend, and can be found at https://bit.ly/2Jx95PV.