Blue Drop · Water dispensing proposal
Blue Drop
A prepaid water system. Customers load a card at the counter, then draw water from a dispensing point. The meter measures every millilitre and takes the cost off the card.
Overview
Prepaid water, measured to the millilitre
Blue Drop is a closed-loop water system. Customers buy credit and it goes onto a DESFire EV3 card. That card runs the dispensing point. The meter measures the water, works out the cost, and takes it off the card.
Because the credit lives on the card, the dispensing point doesn't need a network connection. That suits islands and remote sites.
The short version
- DESFire EV3 cards hold the credit
- Top-ups at any POS terminal
- The meter opens and closes the water
- The card balance updates after each use
How it works
From top-up to water
Six steps, from paying at the counter to the card being updated.
Buy credit
The customer pays at the counter and the credit goes onto a DESFire EV3 card.
Tap the card
They hold the card on the reader at the dispensing point.
Water starts
If there's credit on the card, the meter opens its valve.
Fill up
Water comes out of the nozzle and the customer fills their container.
Water stops
The meter measures what was used, to the millilitre, then closes the valve.
Card updated
The cost comes off the card straight away. No cash, no change.
Components
What's in a dispensing point
DESFire EV3 cards
Prepaid water credit, stored securely on the card itself.
POS terminal
A Nexgo Android terminal reads the card, controls the water and tops up credit.
Water meter
Measures the water to the millilitre, and opens and closes the valve.
Nozzle
The tap the customer fills their container from.
Transaction log
Every top-up and every litre is recorded, so the numbers reconcile.
Why it's built this way
What it solves
No cash at the tap
Customers pay up front, so there's nothing to handle at the dispensing point.
Cards are hard to fake
DESFire EV3 uses AES encryption and mutual authentication.
You bill what's used
Charges match the water drawn, measured to the millilitre.
Works without a network
The credit sits on the card, so dispensing keeps working if the connection drops.
Reusable cards
Top them up again and again at any POS terminal.
A record of everything
Every load and every dispense is logged.
Technical summary
Specifications
Working figures for the proposed system. We confirm the final numbers after the site survey.
| Card | MIFARE DESFire EV3 |
|---|---|
| Card security | AES-128, mutual authentication |
| Recharge | POS terminal top-up |
| Metering | Precision water meter |
| Accuracy | Millilitre (mL) |
| Valve | Integrated in the meter |
| Settlement | On-card, real time |
| Connectivity | Offline capable |
Proposed scope