GeoSIL 150 Water Tank Treatment

GeoSIL 150 rainwater tank treatment is:GeoSIL 150 Rainwater Tank Treatment

  • Non toxic
  • Ecologically friendly
  • Tasteless and odourless
  • AsureQuality approved (Reg. No. 0035)

Water Tank Hygiene

Water is one foodstuff for which there is no substitute. It is a universal solvent, and sustains life forms of all types. For this reason it can be the carrier of all sorts of dissolved materials, biological life forms, diseases, and toxic contaminants. Contamination can include bacteria, coliforms, viruses, cysts, pesticides, and dissolved minerals such as iron and manganese.

Rainwater, once thought to be better quality than town water, healthier, purer, and free of any added chemicals, is increasingly becoming a cause for concern. It can be exposed to many pollutants, such as insects, bird droppings, dust, agricultural sprays etc. Pollutants in a rainwater tank can become concentrated, whereas they may be diluted in a running stream. Giardia is also a real possibility in rainwater tanks, because faecal matter from animals and birds on the roof, and viruses such as Legionella can be carried in the air. Recent studies in New Zealand have shown that more than 50% rainwater supplies are contaminated.

Water Tank Treatment

Treatment of domestic tanks can be difficult because of the many variables, and the way they can change from day to day. Contamination in a water tank can infect the plumbing system of a dwelling, and infections such as legionella can be passed on, not only through drinking water, but through baths and showers as well. An effective, affordable method of treating tanks therefore lies a lot on common sense and the use of an effective treatment program.

Effective treatment therefore usually requires a number of steps to be followed to provide safe, fresh, healthy water, free of the dangerous inhabitants we wish to avoid.

To be suitable for rainwater tanks, a disinfectant should:

  • Be a powerful disinfectant, safe to use and effective against harmful contaminants
  • Provide a long lasting effect
  • Be non polluting to the environment
  • Be approved in NZ for addition to drinking water
  • Be tasteless and odourless
  • Be effective over a wide pH and temperature range
  • Not form any undesirable chemical by-products
  • Leave the water fresh, pure and healthy

Only GeoSIL 150 provides all of these features.

Click to download the GeoSIL 150 Material Safety Data Sheet

GeoSIL 150 Dosage Rates

Estimated Tank Water Qty (litres) GeoSIL 150 Dose in (ml) & litres
Normal Heavy (Shock Dose)
1,000 100 (ml) 200 (ml)
5,000 500 (ml) 1.0
10,000 1.0 2.0
15,000 1.5 3.0
20,000 2.0 4.0
25,000 (5,500 Gal) 2.5 5.0
30,000 (6,500 Gal) 3.0 6.0
Contact Time 24 hrs 24 hrs

Three Step Treatment

  • Step 1
    Ensure that the roof, gutters, down pipes etc. are clean. Drain and flush any low points that can allow dirt and contamination to collect. Estimate the amount of water in the tank (under estimate if in doubt as a modest overdose of GeoSIL 150 is not harmful). Select the dose rate from the chart above, considering the condition of the tank and water and the daily usage.
  • Step 2
    Dose the tank by removing the hatch cover and spreading GeoSIL 150 over as much of the surface of the water as possible. Mix using a paddle or run a hose back into the tank and leave to circulate.
  • Step 3
    Allow contact time for the GeoSIL 150 to mix and react (the water may be used within this time but disinfection may not be complete).

Regularly Dose With GeoSIL 150

Selecting the Dose Rate

  • Normal
    For well maintained tanks under normal conditions, and tanks regularly treated.
  • Heavy (Shock Dose)
    For initial tank treatment, problem tanks, or for tanks not regularly dosed.

NOTE: Depending on the conditions in the tank and the water consumption, GeoSIL 150 can remain active in the water for between 14 and 28 days. Redose as required.

Do's and Dont's


  • have the roof, gutters, tank inspected and cleaned regularly, and keep clean
  • install leaf screens, and "first flush" diversion systems. Drain underground transfer pipes
  • seal all entry points and secure covers
  • consider installing a UV steriliser
  • ensure that the roofing material is suitable for the collection of drinking water


  • allow dirty or contaminated water into the tank
  • use chlorine based products if organic contaminants are likely to be present in the water
  • fill the tank with surface water that may contain soil nutrients, run-off, and decayed animal or organic matter
  • expect the tank to look after itself