If you bake pies at home, you will notice that most recipes for pie crust (pastry crusts, not crumb crusts) give you an approximate amount of water to add to the dough, not an exact amount. This can be frustrating when you are unsure of the correct consistency of the finished pie dough and want to get the recipe done as accurately as possible!
There are a couple of reasons that an exact amount of liquid is rarely given in a pie dough recipe. The primary reason is that adding too much water can make your pie dough tough and once it has crossed that line to being overworked and over hydrated, there is really no recovering from it. Most recipes are designed to encourage you to add the water in as carefully as possible in an effort to ensure that your pie crust will be tender, flaky and delicious. The secondary reason that an exact amount isn’t specified is that it is hard to tell exactly how much liquid a sensitive pastry dough like pie crust will need. Flour absorbs moisture and, not only can different flours absorb different amounts of water, but environmental factors like high humidity can have a noticeable impact on dough when you’re only adding in a few tablespoons of liquid in the first place.
So, although it may be a bit frustrating at first to not have the exact amount given to you, you will end up with a better pie crust when you learn to mix as you go and check to see that the dough really is just coming together (not sticky, but forms a ball easily). By doing this, you will preserve the tenderness of the pie dough that is created by rubbing in the butter or shortening to the flour – and you’ll produce great crusts time and again, even if you need to make a couple of test batches to practice!