Why does my tank
empty so quickly?
An abnormal drop in rainwater is often a sign of an invisible leak or overconsumption.
search Why is my tank emptying quickly?
Did you find that the level of rainwater in your tank goes down abnormally quickly? Don't panic: this phenomenon is more common than is believed and its causes are often identifiable.
An unnoticed leak from the tank, faulty suction strainer, seasonal overconsumption, or a simple error in estimating the available volume can explain a rapid decline. Sometimes an outdoor tap that leaks can empty hundreds of litres in a few days without you realizing it.
In this article, we review all possible causes, detection methods and solutions for restoring a watertight tank.
list Contents
plumbing 1. Detailed causes of abnormal decline
Before you suspect the worst, consider the most common causes of a rapid drop in your tank level.
dangerous Leak in the tank (crack or split)
Cracks in the tank wall, especially on aging concrete or plastic tanks after impact, can cause continuous loss. The buried tanks are particularly vulnerable to micro-cracks caused by ground movements.
troubleshoot Faulty suction strainer
The strainer at the end of the suction pipe prevents debris from entering the pump. If damaged or poorly positioned, it can suck air or allow water to flow continuously, even if the pump is off, by siphon effect.
settings_backup_restore Non-return valve that no longer holds
The non-return valve prevents water from returning to the tank after suction. If worn or blocked, the water goes back down into the tank, giving the impression that the pump is no longer priming properly and that the level is dropping for no apparent reason.
water_damage Leaking outdoor tap
An outdoor tap that is not fully closed or whose seal is worn may lose several litres per hour. This is one of the simplest causes to check, but also most often overlooked. A simple drip can amount to 50 L/day.
water_drop Seasonal overconsumption
In summer, garden watering, car washing or pool filling can quickly exhaust your reserves. A consumption that you think is "normal" can be two to three times higher than the annual average.
ac_unit Evaporation
Above-ground tanks in the sun can lose several centimetres of water by evaporation during hot weather. Even the buried tanks are not completely safe if the inspection hatch or lid is not perfectly waterproof.
lightbulb Tankio tip: Note your weekly consumption for one month. A sudden variation is still suspicious.
health_and_safety 2. Quick diagnostic table
Identify the problem from the observed symptoms:
| Symptoms | Probable cause | Recommended action |
|---|---|---|
| Regular decline even without consumption | Leak in tank or defective valve | Level test without water use + inspection |
| Level drops only when the pump is running | Leaking suction strainer | Check and replace the strainer |
| Water around the tank (buried tank) | Crack in the wall | Professional inspection, possible repair or replacement |
| Increased decline in summer | Overconsumption or evaporation | Track consumption with tankio |
| Continuous flow noise | Leaking outdoor tap | Close all valves and check |
| Slow and progressive decline, wet soil | Microcrack or defective joint | Food colouring test |
visibility 3. How to detect a leak yourself
No need to be a professional to spot an anomaly. Here is a simple 4-step method.
Testing without water use
Note the water level in your tank and then do not use any connected devices for 24 to 48 hours. If the level drops despite everything, a leak is almost certain. With a Tankio connected gauge, this test is automated: the level history immediately shows you an abnormal slope.
Full visual inspection
Examine the area around the tank: standing water, abnormally wet soil, apparent cracks on the walls (for above-ground tanks). For buried tanks, check that the inspection hatch and lid are dry and free of infiltration.
Verification of connections and pump
Inspect all fittings, joints and hoses. A loose connection can be the source of a slow leak. Also check the non-return valve and suction strainer. If the pump is triggered abnormally often, the valve is probably involved.
Food colouring test
Pour a few drops of food dye into the water of the tank near a suspicious joint or a potential crack. If the dye is drawn outwards, the leakage is confirmed. This test is particularly effective for above-ground tanks.
warning Caution: if you suspect a structural crack on a buried tank, call a professional. An empty tank in the ground can cause ground collapse.
checklist 4. Preventive maintenance of your tank
Regular maintenance is the best way to avoid bad surprises. The schedule recommended by professionals is as follows:
| Frequency | Action | Why? |
|---|---|---|
| Every 3 months | Clean gutters and prefiltration filter | Keeps dirt out of the tank and preserves water quality |
| Every 3-4 months | Check and clean the water filter | Maintains flow and protects the pump |
| Every 6 months | Check the pump and non-return valve | Prevents outages and loss of efficiency |
| Annual | Complete visual inspection of tank and fittings | Detect micro cracks before they get worse |
| Every 5 to 10 years | Complete emptying and cleaning of the tank bottom | Eliminates accumulated sediments that can block pipes |
Note: Micro-organisms naturally present in rainwater help maintain clean water by decomposing leaves and organic debris. Too frequent or aggressive cleaning can disrupt this biological balance.
analytics 5. The importance of sensor accuracy
To detect a micro leak, your gauge must be extremely accurate. A float gauge or low-end ultrasonic gauge can have a margin of error of several centimetres, thus masking a slow leak that still significantly empties your tank over several days.
check_circle Hydrostatic gauge (tankio)
Accuracy ±2mm. Measure the actual weight of the water column. No moving parts, reliable in the long term. Detects a leak from the first liters lost.
cancel Classic float gauge
Accuracy from ±2 to 5cm. Mechanical parts liable to wear and jam. May indicate a stable level while the water drops slowly.
lightbulb Did you know that?
A hydrostatic pressure sensor (such as tankio) measures the actual weight of the water column. It is able to detect a level variation of less than 2mm, which is crucial to identify a leak before it empties your tank. For example, a 2 mm/day leak on a 5000 L tank corresponds to a loss of about 25 L per day — 750 L per month, totally invisible without accurate monitoring.
Schematic of a complete rainwater harvesting system with buried tank.
eco 6. Differences by tank type
Not all tanks face the same risk of leaks. The material and installation method directly influence the risks and maintenance.
bungalow Concrete tank
Life: 30 to 50 years. Heavier, more stable. Concrete has a basic pH that naturally neutralizes the acidity of rainwater (pH 5 to 6.5), which is beneficial for water quality. On the other hand, cracks are more difficult to repair and ground movements can cause micro-cracks.
Maintenance: inspection of seals and interior coating every 2-3 years.
inventory_2 Plastic tank (polyethylene)
Life: 20 to 30 years. Lighter, easier to install. Plastic is insensitive to corrosion and roots. On the other hand, it is sensitive to UV exposure (above-ground tanks) and can deform under the pressure of the ground if poorly installed.
Maintenance: check the absence of deformation and the sealing of the fittings annually.
landslide Underground tank
Advantages: space savings, stable temperature (less evaporation), UV protection. Disadvantages: more complex leak diagnosis, limited access, risk of groundwater infiltration. The ground exerts constant pressure that can cause cracks over time.
cottage Above-ground tank
Benefits: simple installation, easy inspection, accessible maintenance. Disadvantages: sensitive to temperature variations (freeze, heat), greater evaporation, visible bulk. Leaks are generally easier to detect and repair.
gavel 7. Regulations and grants in Belgium
The recovery of rainwater is increasingly encouraged — and sometimes made compulsory — by the Belgian public authorities.
Brussels-Capital Region
Since 2023, any new construction or major renovation must include a rainwater tank of at least 33 L per m2 of roof surface. Failure to comply with this obligation is subject to administrative sanctions.
Flemish Region
Premiums exist for the installation of rainwater tanks. Amounts vary depending on the capacity of the tank and the municipality. Check with your local administration to find out the exact support available.
Walloon Region
Regional and municipal incentives are also available. Wallonia strongly encourages rainwater harvesting through "Ureba" premiums and tax reductions for individuals and businesses.
info Grants and requirements are constantly evolving. Consult the official sites of your region for the most up-to-date information.
water_drop 8. How tankio solves the problem
The Tankio connected gauge gives you total visibility on your rainwater consumption. With a hydrostatic pressure sensor of unparalleled accuracy (±2mm), you will receive a notification as soon as a level anomaly is detected.
- checkDaily, weekly and monthly consumption graphs
- checkReal-time alerts in case of abnormal drop in level
- checkComplete history to compare seasons and detect trends
- checkSimple installation without building work — compatible with all tanks