If trying out street food, always stick to something that you can see being
prepared in front of you.
For adventure activities, make sure the provider is experienced, first aid experts, and that there are helmets and buoyancy aids available for water activities. There is still no organization supervising safety standards on the water, so you need to do good research and use a responsible tour operator.
Houseboats have a good safety track-record and all houseboats should have trained lifeguards. But the backwaters are deep, so be careful, especially if non swimmers are on board. Swimming is not recommended unless there are lifeguards present.