They're among items Israel has blocked from coming in on aid trucks.

Water purifiers and medical supplies have also been stopped.

That's according to an Egyptian Red Crescent document seen by Reuters and sources in Gaza.

At the heart of the issue is this question:

Are these items for civilians? Or Hamas?

Israel inspects trucks bound for Gaza and confiscates items it thinks could have both civilian and military purposes...

Or what's known as "dual use" potential.

It's part of a policy that long pre-dates the October 7 Hamas attack on Israel and ensuing war in Gaza.

Israel denies blocking such items.

The issue of which items do or don't get through has become all the more urgent...

as the conflict has displaced most of Gaza's population - and sparked shortages of food, water and medicine.

Among those items are water purifiers.

The Red Crescent document -- which is from mid-December -- says 1,200 of them have been blocked by Israel.

Moheb al-Shaer owns a desalination plant.

He says he hasn't been able to switch filters since the start of the war.

The Israeli Defence Ministry agency that coordinates aid deliveries with the U.N. and humanitarian groups says filters have, in fact, entered Gaza.

It adds over 12,000 U.S. tons of medical supplies have gotten in, too.

"We are not refusing anything..."

Here's Colonel Elad Goren:

"All of those are entering everyday, hundreds of trucks into Gaza. And I hope that the U.N. will increase their capacity to take more and to distribute more."

But doctors working in Gaza tell a different story.

At this facility, an x-ray technician says his hospital is facing a shortage of disks needed to read images.

There's a shortage of dialysis machines, too, according to a patients' spokesperson.

Dr. Suhaib al-Hams chairs the board of directors at the Kuwait Hospital.

"Our hospitals today have become mass cemeteries where hundreds are dying," he says.

It's hard to pin down what exactly is considered "dual use" because there's no public list.

When asked, the Israeli agency referred Reuters to an online document from 2008.