Jeremiah is explaining to the people that instead of trusting in God they are building up cisterns. Warfare in their culture meant laying siege to the city. You could not bring in food or water or go out to get food or water.
It is hard for us to imagine someone laying siege to Rice Lake for two years where all of us would have to survive on the food in our warehouse stores (grocery stores) and our cisterns (water towers) currently. At some point of hunger and thirst we would have to give in to the enemy.
The Israelites were so clever that they dug underground tunnels to divert the water stream outside of their walls to the inside and poured into cisterns. Again, they were relying on their resources and talents rather than trusting in God.
A major problem with cisterns is that they leak. Your water source was always draining away into the ground. A small stream would not be enough to provide water to thousands of people.
The broken cistern passage has always reminded me of the huge baptismal fonts the larger churches have. Some of these fonts are so big you can walk into them. Having a full immersion baptism is impressive. There is only one problem. You may have guessed it. These large fonts always leak.
To keep the water somewhat fresh and clean you need water pumps to move it around. This means there are underwater pipe connections, connections in the bottom or side of the font, and walls of the font made waterproof. Anyone who has ever tried to make anything waterproof knows it cannot be done.
Our baptismal fonts are often our leaking cisterns. I find many priests skip the large baptismal fonts and do baptisms in regular containers such as what we have. It is amazing, but in a small font or a huge font, the baptism is always valid. God is in control.
May the Lord bless you in the name of the Father and of the Son and of the Holy Spirit. Amen