Reserve 1/4 cup of the cooking water and drain the pasta.
After five minutes, ladle out about 1 cup of the cooking water and reserve.
Add some of the reserved cooking water, salt and more lemon juice, if needed.
Remove half a cup of the cooking water from the pot and set aside.
Five minutes before the potatoes are cooked, add the broccoli to the cooking water.
Add the pasta to the pan with the reserved cooking water.
It can also occur with an abundance of iron in the cooking water.
When the pasta is just about done, scoop out a cup of the cooking water.
I always reserve about a quarter cup of the cooking water from the pasta to add to the sauce.
Drain it, reserving about a cup of the cooking water.