Blue Green Algae in a Water Cistern

Blue-green algae, or cyanobacteria, grow in still or slow-moving water. It is buoyant and forms scummy layers on the water called blooms. In addition to blue and green, it can be red, brown or purple. A cistern is a water reservoir used to store water for future use. Over time, it can become contaminated with mould, slime and algae, including blue-green algae. This may cause serious health problems.

History

• There is fossil evidence that blue-green algae has been around for millions of years, and records from 100 years ago demonstrate how livestock suffered from the toxic effects of blue-green algae. It is probable that the frequency and duration of algal blooms is getting worse. According to the Wisconsin Department of Natural Resources, this is due to the use of nutrients in agriculture, increased sewage and phosphorous-based fertilizers and detergents, entering the water system and being found in cisterns.

Dangers

• Blue-green algae is capable of producing toxins that affect people through inhalation, swallowing or contact with the skin. These include dermatoxins and gastrointestinal toxins, which cause headaches, vomiting and diarrhea; hepatotoxins, which cause respiratory failure, tumors and in extreme cases, liver cancer; cytotoxins, which can cause organ damage; and neurotoxins, which affect the central nervous system and are responsible for seizures, paralysis and even cardiac arrest. Water from a contaminated cistern should never be used for bathing, drinking or cooking.

Precautions

• Algae finds it difficult to grow in a cistern that is not be exposed to light. A water aeration system will also help keep water clean and inhibit algal growth. Different systems include an air eduction system, which sucks in ambient air, electric windmills and aerators. These systems supply good bacteria with the oxygen they need to fight algae. Because cold water retains more oxygen than water at higher temperatures, a good precaution against algae is to keep water kept very cold or at freezing point.

Safety

• To avoid contamination, cisterns should be kept far away from sewage lines and on a sloping site so that potentially contaminated surface water can drain away. Cisterns should be inspected and tested for contamination twice a year and thoroughly cleaned every two to five years with a strong chlorine solution. They should be regularly checked for leaks, cracks or breaks, and poor-fitting lids should be replaced. All pumps, gauges and filters cleaned and tested.