I'm worried about your head gasket. The mileage is fairly low for a head
gasket problems, but overheating is both a cause and a symptom of head
trouble. Overheating can warp the head and cause the center of the head
gasket to fail.

A quick test for this sort of failure (typically combustion gasses getting
into the coolant) is to start with a cold car and remove the radiator cap.
Start the engine, pinch closed or kink the rubber hose to the coolant
reservoir and place the palm of your hand over the radiator opening. If you
feel a steady rise in pressure within a second or two - or worse yet,
pulsations from the engine running - it is bad news. If the radiator bubbles
up or disgorges coolant, same thing. If you don't/it doesn't, look for other
causes for the overheating. If the head is warped it can usually be milled
flat to save you the expense of a new head, but there is no way of knowing
it's actual condition without removing the head - a big job.

If the car passes the head gasket screening test (and maybe even if it
doesn't) we need to know: you mention adding lots of water... has the system
had antifreeze/distilled water mixture this whole time or has it had tap
water? Hondas especially don't like tap water.

For the hood release, if you have some spray lubricant to spray on the latch
mechanism - silicone is my preference, but WD-40 will do in a pinch - give
that a try. Also pull on the release lever in case it sprung (is in the
closed position).  If all that fails, the mechanism isn't all that
complicated. It is uncomfortable to look closely at but if you can twist
yourself around to see it you can probably figure out how it should work and
what is wrong. A good start is pushing on the slanty (technical term) part
that gets pushed aside at the very bottom of the latch... it should work
against a stiff spring and then the mechanism should clank closed. Release
it with the release lever. A few minutes investigation should reveal what
isn't working right.

Mike

head gasket or thermostat.  don't drive till it's fixed!  warped heads
are expensive.  follow mike's advice for the quick head gasket test.

1) Does the car overheat when it's idling, or when you're actually moving?
2) Was the rad low when you added water? Does it get low again fairly
quickly?
3) When it starts to overheat, does revving the engine drop the
temperature?

Hood latch may be rusted. Spray with WD-40 & wiggle until it's loose. Then
put lots of oil on it.