Is it dangerous drinking from untreated water supply tanks? Or are they a viable alternative to the treated water in our taps? Here’s what the facts tell us. 

There’s a big “raw water” movement going on at the moment. Advocates will tell you to steer clear of treated water and instead, opt for pure, raw water that’s untreated because it contains minerals that treated water doesn’t. 

While there’s a hint of truth in that, they’re usually talking about pure water from streams that are untouched by civilisation. Drinking from untreated water rainwater tanks, on the other hand, is dangerous. Here’s why. 

What Can Affect Water in Supply Tanks 

Unfortunately, your tank water can easily become contaminated with harmful microorganisms, chemicals, and traces of toxic metals. 

Depending on how your water is collected – a borehole, stream, lake, or catching rain off the roof – animal droppings, leaves, insects, and chemical residues from farmyard runoff could be part of it. 

Your water may also become contaminated by: 

  • Pesticides 
  • Dust 
  • Lead—especially from the flashing on the roof 
  • Fire retardants 
  • Ash and debris 
  • Chemical spraying 
  • Chemical residues from runoff from road 

If you don’t have leaf strainers in place, then leaves, soil, insects, and even mosquitoes can end up in your water tank. This can cause the stored rainwater to be unsafe… Who wants to be drinking insect-infused water? 

The Dangers of the Tank Material 

It’s important to be sure that your tank is made from food grade-material and that there’s no material on the roof – flashing or roofing screw washers – that could potentially contaminate the water stored in it. 

If you have a steel rainwater tank, you’ll want to make sure that it has a food-grade inner poly lining. Not only does this help to prevent the tank from corroding, but it also helps to stop the water from developing a metallic taste. 

When installing the water tank, make sure that tank, pipes, plumbing materials, and the coating have been tested and certified to be in contact with drinking water. 

Ideally, the tanks and materials should meet the following standards:

The PVC-U pipes and fittings should meet the following standards: 

Both these standards mean that the materials used for your water storage tank don’t present a risk of leaching. 

If your water supply tank is connected directly to the plumbing of your house, then you should flush the pipes for several minutes after using the tank water. This will help prevent any metals—lead or copper—from the plumbing leaching into your clean water. 

How Does Treatment Help? 

You may be tempted to drink raw rainwater, especially if you’re worried about how your tap water is treated. But it would still be a good idea to have a water filter installed

Most filtration systems can effectively treat water and remove bacteria and sediment. If it has an activated carbon filter that’s effective at removing chemicals and odours and it will give the water a crisp, clean taste. 

Even if you do have a filter, we recommend putting the following measures in place to ensure that your water in your storage tank doesn’t become contaminated:

  • Ensure that the tank is properly sealed 
  • Keep it out of direct sunlight 
  • Install screens or filters to prevent mosquitos, insects, and leaves getting into the tank 
  • Clean your roof and gutters frequently 
  • Store the drinking water in an above-ground tank 
  • Maintain your water tank and clean it out regularly

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