John explains that for water to change, something has to happen to it. Because the DE1 water tank is not sealed airtight, the water remains exposed to oxygen and stays properly oxygenated. If a user happens to use chlorinated tap water, letting it sit actually allows the chlorine to outgas, making it taste better. Therefore, high-quality water sitting in the tank will not degrade or taste worse over time. The only real environmental concern with an open tank would be a small insect like a mosquito getting inside, which can be solved with a third-party lid.
John identifies two distinct issues that cause water to taste stale in traditional boilers:
Unlike traditional boilers, Decent machines let the water sit at room temperature in the tank and then heat it on-demand under pressure only as it is needed for brewing. This mechanism ensures that the water retains its optimal flavor and avoids both deoxygenation and over-mineralization.
For users with automatic refill or catering kits, the firmware actively manages the water tank to keep it at an absolute minimum level. Instead of filling the tank all the way up to sit stagnant, the system automatically introduces fresh water in small pulses to perfectly keep pace with the active brewing recipe. Because of this, users will notice the machine actively topping up the water tank in real time while an espresso or pour-over is being made.
By keeping the water level at an absolute minimum, the machine has less standing water volume to preheat and produces less overall noise. This approach ensures that water is freshly delivered to the tank exactly when required and is used up almost immediately, preventing it from sitting out.