I have a Honda Odyssey 1999 with 80000.When I should replace the timing...
 

...belt?Do I need to change water pump?

Don't know that exact vehicle but rule of thumb is that if you have to remove the water pump to change the belt or chain then replace the pump. You have done all the work so why stick an old one back on. But at 80,000 miles I would change it for sure.

Honda recommends replace at 90k. ALWAYS change the water pump when u change t-belt. use Honda or gates belt only. also, now is the time to change many things. here is the list: timing belts( there are 2 on 4 Cly.), timing belt tensioners, water pump, cam seals, crank seals, adjust valves, valve cover gasket, thermostat and gasket after flushing cooling system, spark plugs, distributor o-ring(if equipped) and drive belts. service tranny and flush power steering fluid. its a lot to do but my sisters Honda is over 400k miles and still runs like a champ. preventative maintenance!!