here is the explaination

H2O, has its highest density (smallest volume) at temperature 4C (39F). the higher or lower temperature than that point, the lower its density (the bigger its volume). H2O gets frozen at 32F (0C), which is lower than but close to 4C and its density is a little big lower (there is only a little bit expansion). when the temperature goes lower and lower, ice expands more and more. so, your water pipe was broken during the three days with low temperature at 10-20F (-12 - -7C) but the ice in pipe couldn't flow out. when temp was above 32F (0C), the freezing point, ice became water and went out. this also explains why ice floats on water and why fish survives during winter (the water at bottom is always at 4C when there is ice on top).