Most don't have a water reservoir. What looks like a reservoir at first glance is a coil of plastic tubing. Simple to manufacture and few fittings to leak. On the downside, maybe 0.5 litres of capacity and heat transfer is not rapid through the plastic.
My old POS Samsung had a reservoir but that was the only good thing about it. Really is a first world problem, I just need to expend the extra 0.000001 calories to put ice in the water…..from the built in ice maker.