Instantaneous water heater with a power below 1.5kW - are they like that?

I am looking for a flow (non-capacitive) water heater with a power of less than 1.5 kW.
The problem is that in a room where "once a Russian year" someone wants to wash their hands, they must have hot (or even just lukewarm) water available, but the installation will not pull more than about 1kW.

I was looking in various stores and comparison websites and I did not find such a heater.
The use of a capacitive one is uneconomical in this case.

Or maybe one with electronic power control?

Heating 1 liter of water at a temperature of 20 degrees to a temperature of 40 degrees with a 1 kW heater would take 84 seconds (in ideal conditions - no heat loss, 100% heater efficiency, etc.) - for a flow of 1 l / min, 2.1 kW is taken as the minimum .
An option would be a 5-liter capacitive heater, but here too the power of the heaters starts at 1500 W.
However, without the modernization of the installation, it probably will not happen, there may be some DIY.

Let me make it clear - the joke is that you do not need 1 l / min, but a maximum of 0.25 l / min, and you should only heat it by about 10 degrees, because the room is warm (about 22 ° C), and the pipes are placed on the surface, so the water standing in them has a temperature similar to that of the room.

I even looked for some for caravans, but I didn't find one.

I have not come across a cash flow with such low power, and in a way "I'm in the industry".
Or maybe the lowering voltage transformer in front of the heater will work?