Standards for plastic and chemical storage tanks


By Ina Opperman

The drought in parts of South Africa has encouraged people to store rainwater and grey water, but few people know that water must be stored and treated correctly to ensure that it is safe to use.

The recent publication of the South African National Standard: SANS 1731:2017 for polyethylene (plastic) chemical and water storage tanks, is the first step to standardise the storing and treatment of rainwater and grey water. Plumbing Africa asked experts and industry players to explain what these standards are, what they mean, and if they are enough.

Plastic water storage tanks are considered a better choice for rainwater or grey water storage because they are available in more sizes and can be used on any flat terrain, while they are also light and therefore easy to move. These tanks do not rust, and UV inhibitors are added to the plastic during manufacturing to mitigate degradation by sunlight. If a plastic tank is punctured, it is also relatively easy to repair.

Green Tank

A basic tank suitable for rainwater harvesting.
Image credit: ARMSA

“With experts predicting that South Africa’s demand for water will exceed its supply by 2025, making better use of our water resources through rainwater collection and enhanced storage and management will become a critical part of a more sustainable future,” says Wayne Wiid, chairman of the Association of Rotational Moulders of Southern Africa (ARMSA).

John Telford, managing director of Calcamite tanks, agrees. “Even during a good rain season, South Africa’s terrain is not ideal for capturing water and therefore rainwater storage tanks are a smart way to ensure you have extra water for your garden.”

Using grey water and rainwater can also save money on water bills and irrigation. “We flush a lot of useful water down the drain, which can be replaced by grey water. In addition, the average household uses up to 40% of its water for the garden, which can also be replaced by grey water,” Telford says.

However, it is not simply a question of installing a tank and using the water. According to Vollie Brink, an experienced wet services engineer, the plastic storage tank is only one small element of rainwater and grey water harvesting — the other elements needed to complete a system that complies with health and safety standards are most important.

“The National Building Regulations (NBR) determine the standards for everything that is installed on a property. While there is a new tank standard for plastic tanks, there is no NBR standard for the use of rainwater or grey water for domestic use, which is critically important. A NBR standard for the use of grey water and rainwater must still be developed and promulgated as regulations in terms of the NBR Act,” says Brink.

Brink says some municipalities have drafted water by-laws on the use of stored water, issued as guides for how to use this water, but these will have to be withdrawn when a standard is developed and promulgated to allow the building control officer (BCO) to apply and police it. “The question is, why are there no appropriate standards for grey water and rainwater harvesting and domestic water in buildings?”

He emphasises that it is important to understand the hierarchy for establishing these standards. “Health, safety, and economy are the cornerstones of the NBR, and the BCO is the responsible person under the NRCS, which falls under the Department of Trade and Industry, in terms of the relevant Act(s).”

Uses of plastic storage tanks

Plastic storage tanks can be used for rainwater and grey water harvesting, municipal backup supplies, and sanitation applications. Water can be stored above ground where it can easily be connected to guttering through simple pipe networks to fill the tank automatically when it rains. Underground water storage works on the same principle, but the tank is buried and takes up less space. A submersible pump is required to dispense the collected water.

Basic Grey Water System 1

A basic grey water system.
Image credit: Calcamite

Municipalities can install a bigger network of water storage solutions and tanks to collect a greater volume of water, which can be used during a disruption or cut-off from the mains supply. Fully integrated water storage solutions provide a self-sufficient, more automated water collection system from mains supply to a predetermined level, with the remaining volume available to store rainwater. This water is then filtered or sterilised to be used for full domestic water supply.

“The question is, why are there no appropriate standards for grey water and rainwater harvesting and domestic water in buildings?” - Vollie Brink, wet services engineer

Fully integrated grey water harvesting provides household grey water storage for various applications, including watering gardens and flushing toilets. “Polyethylene for plastic water storage tanks can be strengthened and moulded into all kinds of shapes very cost-effectively, making these tanks an economical and effective way to store water,” says Telford.

National standard

ARMSA developed SANS 1731:2017 for polyethylene chemical and water storage tanks together with the South African Bureau of Standards (SABS).

According to Wiid, the tank standard, which was developed specifically for South African conditions, serves as proof that a polyethylene tank has been designed properly and manufactured fit for purpose for the length of its warranty life. “It compels tank manufacturers to conform to global best practice and protects members of the broader construction, architecture, plumbing, landscaping, and built industries, as well as consumers, against tanks of lesser quality.”

The tank standard includes:

ARMSA appointed Productivity Engineering Services and Consultants (PESC) as the independent third-party auditing company for regular audits on the storage tanks manufactured by tank manufacturers who choose to comply.

PESC will issue a certificate of independent assurance of a manufacturer’s claim that its products meet the SANS 1731:2017 criteria, enabling them to market their compliance with an ARMSA/SANS approved sticker on their tanks, as well as using the certificate and sticker in their general marketing programmes.

crocodile tank oz

A bigger storage tank for industrial use.
Image credit: ARMSA

“It is therefore important and advisable for any architect, designer, or wet services engineer to ensure that the plastic tanks they specify should carry the SANS 1731:2017 mark. The broader market should also know that not all plastic tank manufacturers are SANS 1731:2017 compliant and that it is in their best interest to purchase tanks that carry the SANS mark,” Wiid says.    

Available solutions

Plastic water storage tanks are usually used to keep water for daily use in homes as well as for commercial and industrial operations, such as firefighting reserves, agriculture, irrigation, chemical manufacturing, food processing, and the reuse of wastewater. “These tanks can be used to store rainwater captured from roofs during a downpour, or grey captured by connecting tanks to outlets such as shower drains and washing machines,” Telford explains.

Product quality

The quality of water storage tanks is important because it impacts on the quality of the water stored in them, while their durability is a key attribute. Water storage tank quality depends on:

Brink says the temperature in a storage tank must not reach more than 23°C to prevent the growth of legionella; tanks standing in the sun must therefore be protected from getting too hot.

“Water storage tanks made in the process of rotational moulding are stronger and can be manufactured faster and cheaper,” says Telford.

Treating stored water for appropriate use

Brink warns that the risk associated with using grey water and rainwater is very high and it should not be done without proper knowledge and treatment, as well as marking the piping and all the other important technical items.

“Black water is not allowed to be treated on the premises of any building, unless it has no sewer connection. Only seven regulations exist for drainage and the first one states that if a sewer connection is available, it must be used. Treating black water on site is expensive and carries a high risk, which requires skilled management 24 hours a day.”

He agrees that it is important to use alternative water but emphasises that users cannot be exposed to the risk without a proper standard.


The ARMSA/SANS-approved sticker used on tanks that comply with the standard.

Telford says it is important to know the difference between rainwater and grey water to treat it appropriately. “Rainwater contains organic matter, such as leaves and bird droppings from the roof, while grey water contains some chemicals, such as detergent or soap. Black water, on the other hand, contains organic waste and includes sewerage and water from dishwashing.”

Rainwater can be used to flush toilets, wash clothes, water gardens, and even drinking after it is filtered to remove any organic material. Grey water can be used to replenish toilets and run washing machines, but it cannot be used for drinking and cooking, depending on the chemicals in the water. Washing machine water can be used on lawns, but may not be ideal for pot plants or vegetables, although shower water can be used for this, Telford explains.

How grey water is treated before use depends on what it will be used for, says Telford. “If the water will be used to water vegetables, it must be treated to ensure the plants do not absorb chemicals and salt, but less caution is required for other plants. Grey water from a bath or shower will contain fewer chemicals, but grey water must be filtered to create drinking water. No treatment is required for grey water if it is used to flush toilets.”

Grey water cannot be stored, unless it is treated first, because the kind of organic matter in the water is unknown. According to Telford, the organic matter can grow quickly and spread in a tank, while some types of detergents and chemicals can also encourage the growth of organic material, such as algae, which can be poisonous or damage tanks and pipes.

Incorporating plastic water storage into an existing system

Telford says it is better to buy a ready-to-use system than trying to install a do-it-yourself job, to avoid using incorrect fittings and seals. “Only SANS 10400 tanks and SABS-approved fittings should be used for waste water.”

He says SANS 1732 will hopefully deal with all these issues when it is published, but it might still take a few years before it is accepted and launched.


Click below to read the May 2018 issue of Plumbing Africa

PA May 2018