Our water has a weird greenish tint and earthy smell after sitting in storage for a few months. Tank looks cloudy when we shine a light in. What is this thing?

Water storage is a common practice for those who rely on tanks to supply their daily water needs, whether for household use, agricultural purposes, or emergency preparedness. However, stored water can sometimes develop unexpected and unpleasant characteristics over time. One common issue that many people face is the development of a greenish tint and an earthy smell in their water after it has been stored for several months.

When you notice that your water has taken on these attributes and that the walls of your tank appear cloudy when illuminated, it may be cause for concern. These changes are often indicators of biological activity within the tank, most commonly associated with algae blooms. Understanding what causes these changes, how they affect your water quality, and what steps you can take to rectify the situation is crucial for maintaining a safe and healthy water supply.

The greenish tint and earthy smell that develop in stored water over time are primarily due to the growth of microscopic algae and bacteria. These organisms are naturally present in most water sources and can multiply rapidly under certain conditions. When water is stored for extended periods, especially in conditions where sunlight can penetrate the tank, algae can photosynthesize and grow.

The earthy smell is often attributed to the presence of organic compounds produced by algae and bacteria. Geosmin and 2-methylisoborneol (MIB) are two common compounds that contribute to this musty, earthy odor. Even in small concentrations, as low as 5 parts per trillion, these compounds can be detected by the human nose.

Algae are simple photosynthetic organisms that thrive in water with sufficient nutrients, light, and warmth. When these conditions are met in a water storage tank, algae can reproduce quickly, leading to what is known as an algae bloom. There are many types of algae, but those that commonly occur in freshwater storage tanks include green algae and cyanobacteria, also known as blue-green algae.

Algae blooms can occur when the water temperature rises above 20°C (68°F) and there is ample sunlight and nutrients such as nitrogen and phosphorus. These nutrients may come from the initial water source, sediments at the bottom of the tank, or organic matter that enters the tank. When algae bloom, they not only change the color of the water but can also impact its taste and odor.

The cloudy appearance of the tank's walls and the green tint of the water are telltale signs of algae presence. When you shine a light into a tank and notice a diffuse, cloudy appearance, it is often due to suspended algae cells and organic particles. These can scatter light, making the water appear murky.

The green tint specifically points to the presence of chlorophyll, the pigment that algae use to capture light for photosynthesis. Depending on the concentration of algae, the water may range from a light green hue to a darker, more intense green. Monitoring these visual clues over time can help determine the severity of the bloom and guide the necessary interventions.

Several factors contribute to the proliferation of algae in water storage tanks. Long-term storage without circulation can lead to stratification, where temperature layers form, creating a conducive environment for algae growth near the surface.

Sunlight penetration is a critical factor as it provides the energy required for photosynthesis. Tanks that are exposed to direct sunlight or have translucent covers are more susceptible to algae growth. Additionally, higher temperatures accelerate both the metabolic rate of algae and the chemical reactions involved in photosynthesis, facilitating rapid blooms.

Nutrients like nitrogen and phosphorus are essential for algae growth and can enter the tank through various means. They may be present in the original water source, introduced through organic matter like leaves and dust, or leached from sediments at the tank's bottom.

The materials used in constructing the tank can also affect algae growth. Tanks made of porous materials or those with cracks can harbor sediments and microorganisms that contribute to nutrient availability. Ensuring that tanks are cleaned regularly and maintained properly can help reduce these nutrient sources and prevent discoloration.

While not all algae are harmful, certain types can produce toxins that are dangerous to human health. Cyanobacteria, for example, can produce microcystins and other toxins that pose serious health risks if ingested. Symptoms of exposure can include skin irritation, gastrointestinal issues, and more severe effects such as liver damage with prolonged exposure.

It's important to note that even non-toxic algae can affect water quality by causing unpleasant tastes, odors, and visual appearance, making the water undesirable for consumption. Therefore, it's crucial to address algae contamination promptly to ensure safe drinking water.

To confirm the presence of algae in your water tank, you can perform several at-home tests. A simple visual inspection, as previously mentioned, can provide initial clues. For more confirmation, collect a water sample and let it settle; if a green layer forms at the top or bottom, algae are likely present.

For more detailed analysis, test kits available from water testing suppliers can detect specific algae types and their concentrations. These kits often measure chlorophyll levels, which can indicate the presence and abundance of algae. While professional testing provides the most accurate results, these home tests can help you gauge the severity of the situation.

Once algae presence is confirmed, it's crucial to clean and disinfect the tank to restore water quality. One effective method is to 'shock' the tank with chlorine. The World Health Organization recommends using a chlorine concentration of 2 to 3 mg/L to disinfect water storage tanks.

After chlorination, the water should be allowed to sit for at least 24 hours before being flushed out. It's essential to scrub the tank walls to remove any biofilm and rinse thoroughly to ensure no chlorine residue remains. For tanks where chlorine is not suitable, alternative disinfectants like hydrogen peroxide can be used.

To prevent future algae blooms, regular maintenance and cleaning schedules are vital. Tanks should be cleaned and disinfected at least once a year, or more frequently if algae issues persist. Installing a filtration system can also help, particularly one that includes UV sterilization, which can kill algae and other microorganisms.

Additionally, minimizing sunlight exposure by using opaque tank covers and ensuring proper tank insulation can reduce the conditions favorable for algae growth. Monitoring nutrient levels in the water and controlling sediment accumulation can also help maintain water quality.

If algae contamination persists despite your efforts, it may be time to consult a professional. Water quality experts can conduct thorough inspections and offer solutions tailored to your specific situation. They can also provide advanced testing to identify any harmful algae species present.

In some cases, persistent algae problems may indicate structural issues with the tank, such as leaks or material degradation. If a tank is beyond repair or consistently fails to maintain water quality, it may be time to consider replacement. A professional assessment can help determine the best course of action to ensure a reliable and safe water supply.