will a 5 watt solar panel charge my 12 volt battery enough to turn on the water pump in my rv?
A lot depends on total usage of the pump. 5 Watts is at best marginal even for a small pump. A 15 Watt panel would be almost adequate. 30 Watts would likely work the best. This assumes an on demand pump rather than one that holds pressure on the line.
At 30 Watts, you are producing only 2.5 amps on a 12 volt system. This enough to replenish the charge on a fully charged battery in light usage.