My Opel Astra van 1.7 keeps blowing steam from exhaust and overheats after about 30 miles

When I pull in and fill the coolant tank with water and wait a few minutes she is grand again but as soon as I pull off again it blows a huge cloud of steam from the exhaust yet again. Its as if its evaporating the water that ive just put into it. The van was parked up since last october so yesterday I bought a new battery and it started right away but now there is an orange light on in the dash with a little tap like symbol in it so im completely stumped and need help BIG TIME thanks for taking time to read my problem guys