This is a very common problem, this happens due to the hard water (tap water ) deposits calcium in the tubing or more commonly in the jet/shower head. This blocks or restrict the water flow. If both jets are not flowing water then it is wise to check the pump first. You can do that by putting the car in ignition without starting the car, allowing you to pull the lever for the wiper and mist/jet mode. Hear for any pump noise, if there is in fact noise coming that sounds like a pump, then your fluid pump is working. (NOTE* It's best to pull up the wipers during testing to avoid scratching the windscreen.) This means that there is infact blockage in the system. If only one of the jet is not working then please skip this step. To clean these jets poke the outlets(holes) with a pin cleaning out any debris, this should work for mild build up. If that doesn't work then you will have the take the jet out and clean it from both outlet and inlet sides of the jet. An easy way to do that is the same pin method, or you can let them soak in vinegar to dissolve the calcium deposits. One some cars like toyota corolla, taking the jets out is rather easy, however on cars such as honda reborn you will have to remove bits of plastic trims to reach the jets as they are not mounted on or under the bonnet.