The Welsh Government is stockpiling body bags in an effort to minimise disruption in the event of a no-deal Brexit.
The poll showed 89% of people who said they would vote Conservative in a general election were in favour of a no-deal Brexit.
Mr Waters tweeted, "I wonder if they know the Welsh NHS are stockpiling bodybags in readiness?"
The Welsh Government confirmed it has spent a "significant amount of money" stockpiling a range of medical supplies. Money, which is said, "could have been used elsewhere in our NHS".
"This includes additional stocks of body bags", it added. "Only last week, the outgoing Chief Medical Officer for England warned that lives would be put at risk as a result of medical shortages following a no deal Brexit.
“We are doing everything we can to manage the significant impact a no-deal Brexit would have on Wales, but all our preparations will not prevent the devastating consequences of leaving the EU without a deal.”
ITV Wales were given access to a "secret warehouse" in April where £4m worth of NHS supplies were being stockpiled.
It contains crates of medical gloves, swabs for x-rays to baked beans and tinned tomatoes.
Boris Johnson is running out of time to get an agreement in place so it can be approved by European leaders at the Brussels summit starting on Thursday.
A Number 10 source said progress was still being made in the talks, which ran to about 1.30am in the Belgian capital and will resume on Wednesday morning.