Guides

Find hidden leaks with the night-flow test

Kanari · 7 November 2026

Leaks are easiest to see when nothing else is using water. In a hotel that's the middle of the night; in an empty villa, any time. The night-flow test uses your water meter to measure what flows when it shouldn't.

How to do it

1. Pick a quiet window, for example 1 AM to 4 AM, when the kitchen and laundry are closed and few guests use water.
2. Read the meter on the line that feeds the rooms (or the main meter) at the start, and write it down with the time.
3. Read it again at the end.
4. Divide the difference by the hours. That's your night flow.

A worked example

At 1:00 AM the meter reads 48,210 gallons. At 4:00 AM it reads 48,390. That's 180 gallons in 3 hours, or 60 gallons an hour, all night, with the hotel asleep. Repeat the test on a second night before acting: one guest filling a bath can skew a single reading.

If the meter is on the city supply rather than the rooms line, remember that a roof tank refilling through its float valve also shows as flow. Note the tank levels at the start and end too.

What the number means

A small hotel at night should use very little: an occasional toilet flush, an ice machine. If the flow is steady through every hour, something is running continuously. A single running toilet can use well over 100 gallons a night.

Narrow it down

• Close the valve to one building or floor at a time and watch the meter.
• Put a few drops of food colouring in toilet cisterns; colour in the bowl after 15 minutes means the flapper leaks.
• Check float valves on roof tanks and cisterns for overflow.

Do it every night, automatically

A meter with a battery reader sends its count every few minutes, so the test runs every night by itself, and your team gets a message when the night flow is too high. See the water meter.