The Bathtub
A bathtub with the tap running and the drain half open. You cannot work out the water level from the tap alone — and every backlog, reserve, hiring pipeline and queue in your organisation is this bathtub.
Your support queue holds 2,000 open tickets. New tickets arrive at 100 a week. The team now closes 105 a week — they have finally overtaken demand, and the slide says "we have turned the corner". Assuming nothing else changes, how long until the queue is empty?
Show the level as a table
| Week | Level |
|---|
The pipeline that never fills
Headcount is a stock. Recruitment is the tap and attrition is the drain, and attrition is almost never in the plan. Hiring twelve to grow by twelve works only if nobody leaves, which has never once been true.
Profitable and insolvent
Cash is a stock; revenue and costs are flows. A business can be profitable on the flows and still run out of the level, which is why "we are profitable" answers a different question from "can we make payroll in March".
Technical debt
Debt accumulates from shortcuts taken and drains through deliberate repayment. Teams track the tap — shortcuts this sprint — and almost never measure the level, so the first honest measurement usually arrives as a crisis.
Attention is a bathtub too
Commitments arrive faster than they complete, and the level is what you carry around. Saying yes is the tap. Nobody ever drained a full tub by opening the tap more carefully.
Before you argue about a backlog again, ask for three numbers: what is arriving, what is leaving, and what is sitting there now. The level is set by the difference between two rates, and almost every conversation about a queue is about only one of them. A team that closes more than arrives is not a team that will clear the queue this year, and the arithmetic that shows it takes about ten seconds.