sirdnA

Water is made of hydrogen and oxygen, which is fuel for the Sun’s fusion. But more importantly, the extra mass also makes the Sun heavier. This crushes it together more tightly and makes fusion happen faster. This means it will burn more brightly and run through its fuel more quickly.

As you keep adding water, the Sun will go through a lot of wacky fusion phases. (During one phase, called a helium flash, the reaction rate is proportional to the 40th power of the temperature—which is probably the largest exponent I’ve ever seen in a physics equation!)

But one way or another, eventually the whole thing will collapse in on itself, blow off its outer layers, and become a black hole. This black hole will keep soaking up water, spraying off X-rays in the process, until finally the municipal water department notices what you’ve been doing and shuts off your service.