What % does water expand per degree when warmed?

Answer

Dear Ronny,

How much the water expands is related to the concept of coefficient of expansion. You can find an explanation about this here:
http://nl.wikipedia.org/wiki/Uitstellingsco%C3%ABffici%C3%ABnt

The (volumetric) coefficient of expansion of water at 20 degrees Celsius is γ = 0.21 10^-3/k

The unit Kelvin (symbol K) is the temperature in degrees Celsius to which you add 273.

This means that if the water increases by 1 degree (ΔT = 1 K), the relative volume change is ΔV/V = 2.1 ten-thousandths.

The water will therefore expand by 0.02% when the temperature rises from 20 to 21 degrees Celsius.

Kind regards,

Laurent Vanbeylen