My home-made-from-garden-hose radiator hose has done a few hundred K without any sign of failure, but had a slight leak under pressure where it joins the radiator, perhaps because its a little too wide, and or isn't as soft/compliant as the real thing.[You must be registered and logged in to see this image.][You must be registered and logged in to see this image.]
Since I've now got the right hose, and there was rust where it was leaking, I flushed the system (forgetting to do the heater, so I'll have to do it again, DUH!) replaced the coolant (with "green stuff", possibly RT-Mart own-brand. labelling all Chinese with no recognisable specs on it, so I'll have to regard it as short-life) and replaced the hose. There was fine rusty sludge in the coolant, and a few scale flakes flushed out of the bottom of the radiator.[You must be registered and logged in to see this image.][You must be registered and logged in to see this image.]
While I was doing this I noticed another teacher here with the bonnet up on her Skoda. This is so unusual in Taiwan I went over to see that she was topping up with plain water. She said it'd had a slight untracable leak after being hit by a motorcycle. They replaced the radiator (can't imagine anything else would be vulnerable to a bike strike) but the leak persists. Since I think I saw her doing this about three years ago, it seems likely that the system has been running plain water for some time. Of course there's no need for anti-freeze here, but I'd think there'd be a risk of long term corrosion damage.
If I had an unfixable leak on a truly disposable car I might put a pinch of washing machine powder in it from time to time, but its hard for me to regard a shiny 10-year old Skoda as quite that disposable, even though that's as old as Taiwan cars usually get.
Might offer her my old coolant once the rust has settled out of it (hence the question). The shock-horror-disgust effect of that might induce her to get the leak fixed.