I purchased this for my husband who is an avid camper. He goes with our teenage boys camping and they all come back smelling horrific (because they shower very little if at all - camp site showers are pretty disgusting!) I bought this thinking they'd have no reason to come back smelly! I hadn't thought until pointed out to me that they were not going to undress completely on a campsite. It did work well for cleaning up after swims in the sea or in rivers (washing with swimming gear on so it all doesn't smell) it does take a good few hours to warm up at all and does need sun to be warm, in an overcast day it didn't warm up much.
Surprisingly the best use my husband found was using it to wash dishes. Much of what they eat when camping is sandwiches, eggs, bacon etc. they'd wash plates and cups using this but then wash the main pan at the campsite wash up. They did this as the plates and cups weren't that dirty and required little soap. The pan needed more and they didn't want to use loads of soap on the ground around the campsite.
I used it a few times to water plants outside (but not with heated water) an also to wash some things outside (outdoor play house and bikes and heated the water for this and it worked well for me)
I was pleased at least I didn't have to deal with everything stinking of sea water! I would recommend - just be aware you need direct sunlight and at least a few hours before use.