WHY are reservoirs so dangerous? Yes, I know they’re cold and deep but so is the sea.

And in Scotland, we’re encouraged to take a bracing dip there whenever the sun appears. What if I told you some reservoirs have underwater machinery that can crank into action without warning, creating huge currents?

It’s a vivid picture and I only know about it because I made a call this week to some experts. I couldn’t get my head around how those picturesque calm waters could take so many lives.

The families of Sean Marshall and Ross Munn who drowned this week in Ayrshire know all about the dangers of reservoirs as they mourn their young men.

Open water terrifies me, as does the prospect of being trapped in a discarded fridge, driving without a seatbelt and switching on a light if I smell gas.

Those of you of a certain vintage will have noticed a common denominator in those fears – each was the subject of a public information film in the 1970s, many featuring a boy called Tony and Charley the cat.

These short films , with the catchphrase “Charley says”, were shown between programmes and used humour or terror to encourage a generation to stay safe.

So why have they disappeared from our screens? Why in the era of You Tube don’t we see 21st-century adverts being used to as good effect?

Why don’t the various TV catch-up sites slip in well-made, 30-second warnings that could save a life? I’d imagine that graphic footage of a huge riptide-creating machine in the dark waters of a reservoir would stay in any kid’s memory for a long time.

We live in such a visual age that it seems strange that the whole idea of the public information film has been consigned to the archives rather than being exploited to its fullest potential – and not just to warn of physical dangers, like drowning.

The suicide of 14-year-old Hannah Smith last week was thought to be caused by so-called internet trolls. Appalled adults can discuss ways of combating trolling but forums in Westminster might as well be on the moon.

It’s the web itself that should be peppered with intelligent warnings, with hard-hitting videos made to appeal to savvy teens about what they’re getting into and how to deal with it.

Such films could be government-funded or paid for by public-spirited commercial companies. They could pop up on media websites that attract huge numbers of kids. As for hammering home warnings to really young kids, TV is still good way to reach such a captive audience.

It’s argued that the death of the public information film is partly because, on TV nowadays, time is money.

Well, maybe it’s time for the goggle box to show a bit of responsibility.

Which would you rather have – another inane trailer for a game show or soap or a two-minute warning that will live with your child for a very long time?