@mfalkvidd Thanks for your time and your warning....
My problem with mysensors is that the only way I know to collect the data received by the GW through mysensors is domoticz, and domoticz reports data to me every 5 minutes. I like to monitor the data through internet, together with meteo, home temperatures and so on.
But a 5 min period is not frequent enough to show me the progressive change in the water level when the pump is working (the average duration of a period of powered on pump is most often a handle of minutes) : to achieve this, my node samples and sends data to GW approx every 5 seconds and it is frustrating to find data in domoticz only every five minutes.
To cope with this issue, I have presently a second -independant- pair of arduino linked by nr24 protocole : one of them collect the data and send them every 5 secondes to the 2nd arduino which starts electromechanical timers cumulating the working time of the pumps with sufficient reliability and accuracy. This cumulated time, cross checked with meteo data and water level, is useful to me to verify that the pumps are working normally. The problem is that I do not know a way to access these info via internet.
So my today situation is that I have, working in parallel, the mysensors system, opened on internet but poorly reactive, and the nr24 system, accurate enough, but that I can only read when I am at home.... Fortunately, presently, these two systems work in parallel apparently without interfering negatively....
My dream would be to unify the two systems....

Thank you for these info. I will have a look on tutorials on scripts and lua in Domoticz. Not so obvious at first glance ! I will need time....
Thanks again.