How to Manage a Rain Water Tank

How to Not Get Dysentery from your Rainwater Tanks

A clean rainwater tank is a safe rainwater tank

Collecting and storing rainwater is an ancient practice. It is very common in rural Australia where access to treated scheme water is not available. The common belief is that rainwater is a safe source of pure water. This may be true as the rain falls on your roof, but if you do not manage your rain water tank correctly, you may well be drinking contaminated water. What is so pure and clean about water that collects bird poo, dead frogs and chemical dust and leaves and stores them all, slowly putrifying in a stagnant pool? The main house rainwater tank at Morilla was an ancient concrete structure that did not seal properly and the collection surface was the large shed - the gutters of which were filled with debris. What it needed was to be replaced with a new tank, but instead we decided to drink bottled water, fit an extremely high quality water filter for cooking water and use the tank water only for showering and flushing the toilet. The water surprisingly remained clean and odour free while we lived there, and no doubt any other farmer would have drunk it without a second thought. Maybe it was my nursing past life coming back to haunt me, but I could never bring myself to just drink water straight from that old, unsafe tank. Farmers all around told us that rainwater tanks are ‘self cleaning’, although how this could possibly occur still escapes me. How does a tank clean itself? The only rainwater tank I would trust would be a brand new one I installed and maintained. Then I could be assured of the quality and safety of the water contained within it.

Water in rainwater tanks is not treated with chlorine as the water that comes from the scheme water system is. This allows microbes to breed and thrive in tanks that are not correctly maintained. What you effectively have is a collection of stagnant untreated water that sits in a tank year after year. The tank will collect debris from roofs and gutters including bird faeces and chemical dust which can pass through a leaf net system, and if the tank is not fully sealed, animals will find their way inside and drown. Over time a sludge will form on the bottom of the tank and if this sludge rises to the outlet point, you will be drinking water that contains some of this sludge material. If at any time the water is not clear, odourless and tasteless, you have a problem with contamination. You do not want to be drinking this contaminated water, and you do not want to know what is in it that has lead to the contamination!

To ensure a pure and safe supply of drinkable rain water for your home, you need to carry out proper rainwater tank, roof and gutter maintenance. If you are collecting your water on a dirty roof covered in chemical spray drift and bird faeces, the water is running through gutters full of leaf debris and dead rodents, and then flowing straight into your tank without going through a first flush system and a leaf net......well, you might as well be drinking out of a ditch. I believe that if most people in rural Australia actually saw what was in the sludge at the bottom of their tanks they would never drink from a rainwater tank again!

Water collected in rainwater tanks is not as safe to drink as treated water that comes through the scheme water system. Scheme water is treated and filtered to meet Australian standards for potable water- drinkable water and water able to be used in food preparation. The water in a rainwater tank is completely untreated and will have a higher microbial content than scheme water. Furthermore, it is up to the individual home owner to maintain the water quality and safety.to ensure the microbial levels are kept at an acceptable level. Many of these microbes are harmless, but some can cause illness if the water is used as drinking or cooking water. The purpose of having a safe and suitable collection system and tank and carrying out regular maintenance of your tank, roof and gutters is to keep the microbial population as low as it can possibly be. I can hear all the people who have rainwater tanks now- “I have never been sick because of my rainwater tank, and neither have any of my neighbours!” It is true that reported cases of illness from rainwater tanks are low, but cases have occurred where rainwater tanks have been contaminated with Salmonella and Campylobacter and Escherichia Coli from bird and other animal droppings and the people drinking the water from those tanks have become ill from drinking the water. A low report rate does not mean that illness from drinking rainwater tanks does not occur. It is quite possible that some people who develop sporadic or isolated episodes of diarrhoea, gastric upsets, nausea, headaches or general feelings of being unwell, may well be affected by their contaminated rain water and simply be unaware of it, and therefore not seek medical advice, or not mention the rainwater tank to their doctor. The doctor may also not think about the possibility of the rainwater tank being contaminated and therefore pass the illness off as ‘gastro’. The contamination may only occur when the water in the tank is disturbed and the sludge at the bottom is agitated, or when a new influx of microbes enters the tank, such as after a heavy rain. This may be the only time some people notice the ill effects of the water they are drinking. Regardless of whether the rate of illness is low or not, you most probably do not want to become a statistic, and you will want to protect your family from illness associated with poor maintenance of your tanks. Prevention is better than cure. I also believe that regardless of the reported rates of illness from rainwater tanks, few people would actually want to be drinking water that was awash with faeces, dead animals, rotting leaf matter and chemicals.

What are the hazards and risk associated with rainwater tanks?

Contamination of collection surface:

Rainwater is collected from a surface where it is allowed to run off into the tank. The largest risk of introducing chemicals, microbes and debris into your tank will be here, on the collection surface. Most commonly, rainwater for domestic use is collected from rooves and gutters. The roof is a large surface area which is easily contaminated with potential pollutants, pathogens and debris. Birds land on rooves and drop faeces. Insects crawl on rooves and die. Rodents forage through the debris collected from trees in the gutter. Frog live in puddles formed by the accumulation of leaves in the gutter. Chemical sprays may drift from the paddock to the roof top, or be dropped from crop spraying planes. Exhaust fumes from trucks and other machinery may settle on the roof if the machinery is utilised nearby. Any fumes from factories, generators, or workshops may also find their way to your collection surface. If you have an open fire, especially a slow combustion fire, and the chimney fumes are expelled onto the roof you are collecting water from, you will be contaminating your water supply. All of these contaminants will wash into your tank when it rains, unless you have a first flush system in place. Check your gutters regularly and clean them often. An accumulation of leaves and other debris not only increases the risk of ill health they can also cause the water to develop an unpleasant taste making it less drinkable.

Make sure all parts of your tank are completely sealed

Toxic collection surface:

The roof and gutter material can also be a source of contamination, especially if they contain any lead or lead based paints, or any other hazardous materials. Do not install a rainwater tank on a roof or gutters that contain lead or other toxic metals. Check that the roof and gutters are not painted with lead paints or any bitumen based products. If you paint your roof and have a rainwater tank attached to this roof, do not collect the first few rains worth of water. This should allow any chemical residue in the paint to wash away and not into your tank. Concrete and terracotta tiles are considered safe as a collection surface, although the oxides used to colour the tiles may erode over time and wash into your tank. This may give the water a slight colouration. This oxide is considered non- toxic.  The new zinc and steel roofing materials, galvanised iron and plastic and fibreglass sheeting are all considered safe to use as a collection surface. Asbestos roofing is considered safe to use as a collection surface as the fibres are dangerous when breathed into the lungs not swallowed into the stomach. You be the judge. If the asbestos roof is old and deteriorating you may be better off having it removed professionally and replaced. Treated timber, such as wood treated with copper chrome arsenates, boron and creosote, can also contaminate your tank if the water comes in direct contact with the wood.

Make sure rooves and gutters are kept clean and not exposed to toxic dusts or chemicals

Tank material:

When you install a new tank buy one that complies with the Australian guidelines and you will not be exposing yourself to the risk of chemical contamination. New tanks can impart unpleasant or noticeable taste to the water, such as a metallic taste from a new galvanised tank, or a bitter lime taste from a new concrete tank. If the flavour is too unpleasant the tank may need to be emptied and refilled. This water can be used for purposes other than drinking and cooking. Of course, you can also fit a water filter to your rain water tap and this will eliminate many problems associated with using a rainwater tank, including contamination by microbes, chemicals and unpleasant smells and tastes.

Dead animals in the tank:

If your tank is not completely sealed off to animal entry, you may experience the unpleasantness of having an animal enter your tank and possibly drown. A dead animal in the tank will cause water contamination. The animal may foul the tank with faeces before it dies and once it dies it may swell up and rupture releasing its bowel contents into your tank. Usually you will taste or smell the contamination from a larger dead animal, such as a possum, in the water when it comes out of the tap. Sometimes you will see evidence of the dead animal when you detect fur in your glass of water. As you can imagine, this would be a highly nauseating experience. Smaller animals, such as frogs, may go undetected. Ensuring your tank is properly sealed around the lid and access port is very important. It is also important to have a leaf catcher basket with insect proof netting over the water entry point. This net will catch all the debris that washes along the gutters and downpipes when it rains. A leaf basket and netting also prevents animals from entering the tank via the water entry point. If you have a water overflow point, you will need to cover this with netting too. The leaf basket will need to be checked and emptied regularly, possibly weekly or monthly to ensure it does not become congested and water is unable to flow in to your tank. Check all the insect proof netting regularly to prevent access to your tank by insects.If you find a dead animal in your tank you will need to empty the tank and clean it. If you are unable to do this, remove the dead animal and disinfect the water with chlorine, according to manufacturers instructions. If you were the one who had to remove the animal you may find it difficult to drink from the tank!

 Chemical contamination:

If you live near an area of high vehicle traffic, or industrial area where there are emissions of chemicals from factories, you may find your tank contaminated by chemicals associated with these activities. Fitting a first flush system will reduce the pollutants that make their way into your tank. This is also true for agricultural chemicals that are sprayed near your property and can drift onto your collection surface. I had to laugh when a (not so bright) neighbour in Morilla told me that when they have their canola aerial sprayed they ask the pilot to turn off the spray over the tanks and dams. Really? Is this not expecting the pilot to perform a miracle? How can he control where the wind blows the spray? Your collection surface will most probably become contaminated with chemical drift if you spray chemicals on your property.  A first flush system allows the first rains to wash the collection surface of these contaminants and empty them onto the ground or into drains instead of into your tank.

Mosquitoes:

Rainwater tanks provide an ideal place for mosquitoes to breed. Keep all entry and exit points on your tank covered with insect proof netting. Check your tank for signs of mosquito larvae every few months. You can treat larvae infested tanks with small amounts of medicinal paraffin or even small amounts (1 teaspoons to a 1 kilolitre tank and 3 teaspoons to a 10 kilolitre tank) of domestic (not industrial or commercial!) kerosene to kill the larvae. Kerosene should not be added to plastic tanks and should never be able to be tasted in the water. If you can taste the kerosene, you went too far with the insect control strategy, and you will need to drain and clean your tank. Never add kerosene to tanks with low water levels. Do not add pesticides to your tank water to kill mosquitoes. Personally, I prefer to prevent mosquito access in the first place! Mosquitoes are a real problem, not just because they can potentially spread disease. They are an irritating annoyance on those warm summer nights when you are trying to enjoy a BBQ with friends. You do not want to be breeding your own problem parasites!

Make sure all open ports (overflow port) are covered in fly mesh to prevent insects and animals from entering tank

Poisonous plants:

It is always best to prune any tree near your tank or collection surface to prevent leaves falling into the gutters and deny birds perches over your catchment area. Check the trees you have growing near your tank and collection surface and make sure none are poisonous, such as oleander or yew, for example. If in doubt cut the tree away from your tank and rooves. If your tank is sealed and you have a leaf basket you should not have a problem, but better to be safe than sorry. It may be hard to explain why your husband has died from oleander poisoning when you are perfectly well, and the old ‘leaves in the rainwater tank’ might just seem a little convenient to the investigating police officers.

Know what plants are growing near your tank, prevent any plant parts falling into your tank, fix any breaks in the pipe straight away- unlike here where a spider has made a web and caught several leaves! The gutter is not even connected to the tank!

Sludge on the bottom of the tank:

Sludge will accumulate on the bottom of your tank over time, no matter how well you maintain your tank and collection surface. The better you maintain your tank, the longer it will take for the sludge to rise to a problematic level. Sludge can contain many chemicals and pollutants and you do not want it to accumulate to such a level that it actually rises to the point of water exit to your household taps. The point of water exit is usually low down on the tank, not at the bottom, to avoid drawing the sludge into the household pipes, but low enough for sludge to eventually build up and enter the pipes. You will need to empty and clean your tanks from time to time to ensure you remove this sludge before it reaches your exit pipe. Check your tank every 2 years and if the sludge has completely covered the bottom of the tank you will need to empty the tank and clean it out.

Most outlet ports are low on the tank, so make sure you monitor your sludge build up and remove the sludge before it reaches your port

Stagnant Water in pipes and gutters:

Allowing debris to build up allows water to accumulate in pockets and stagnate. Stagnant water can allow slimes and algaes to grow and these can cause ill health as well as unpleasant smells and tastes in your water. Keep all your gutters and pipes clean and free of debris build up. Any pipes that naturally collect water and do not flush fully after a rain event, such as U bends should be removed if possible or opened, drained and cleaned regularly via the access port. Also tanks that allow light to enter can encourage algae growth- another reason to cover and fully seal your tank. If you smell a rotten egg or sewerage smell from the water in your tank it may indicate that the water is contaminated with microbes and the tank will need to be emptied and cleaned or disinfected with chloride, as per manufacturer’s instructions. Fishy, musty or rotten vegetation smells may indicate algae growth. This will also require emptying or disinfecting. Small white flakes in the water also indicate that microbes are active in your tank. Again, disinfect with chlorine. A fitted water filter at the rainwater tap inside the house will help prevent these contaminants going into your glass!

Wall slime:

All tanks will develop a growth on the sides of the water tank below the water line in time. This is a harmless microbial growth and requires no treatment.

Managing your tank

Chlorination of water:

Sodium hypochlorite or calcium hypochlorite is available from some supermarkets, hardware stores and most swimming pool shops. Regular chlorinating of your tank is not considered necessary and chlorination is only required if your tank is contaminated with organic matter, such as microbes or algae or an animal has been in the tank. Chlorination only disinfects the water held in the tank at the time of chlorination. Water collected after will not be disinfected. The chlorination process will not make the water undrinkable but it will change the taste and smell. The taste and smell should disappear over several days as the chlorine dissipates from the solution. If in doubt about the microbial content of your water and you have are unable to empty and clean or chlorinate your tank, you will need to boil any water from the tank that you intend to drink or cook with.

Water filtration system:

You can use a water filtration system to reduce the risk of microbes, chemicals and pollutants coming out of your drinking water tap. Use the filter according to manufacturer’s instructions and replace filters as required. Dirty or clogged filters will not protect you!

Water filter- make sure the filter cartridges are changed regularly 

First Flush Diverters:

This system allows the first water flowing after a rain to bypass the tank and instead flow onto the ground or into the drains. This prevents most dust and dirt on your roof and in your gutters from entering your tank. As you will be unable to wash your collection surface prior to each rain, this is the best alternative to reduce the amount of bird poo, insects and dust from flowing straight into your tank. This system does not replace the need for regular cleaning of your gutters and checking of your collection surfaces and tank! A first flush diverter is installed in the downpipes before the water reaches the tank. The first flush diverter is a pipe that drops vertically from the collection gutter, and it has a floating ball inside it. As the first water is delivered to the tank, the water runs into the vertical pipe and raises the ball to the top of the pipe, which then closes off the first flush diverter pipe. Any subsequent rain is then delivered into the main tank. The first flush diverter has a very small drainage outlet port in the bottom of it, which allows water to very slowly drain from the first flush pipe. This ensures that the ball stays in the closed position when it is raining, but opens again when the rain stops.

First flush diverter- the first rainfall will clean the dust and debris off of the collection surfaces and be emptied onto the ground before it reaches your tank.

Cleaning your tank:

 If your tank needs emptying and cleaning because it has been contaminated, you will need to drain it, remove the sludge on the bottom and clean the inside. Be careful not to remove the protective coating on the inside of the tank with harsh scrubbing. You can employ a tank cleaning service if you are claustrophobic and unhappy about getting inside a confined area. If you live in a very isolated area you may have to do it yourself. Make sure you have another person with you. Do not enter the tank without a buddy around to rescue you if you need help. The tank should be rinsed well of all cleaning products before it is allowed to refill with water. Do not put waste water containing cleaning products into the garden.

If you are cleaning your tank to remove the sludge on the bottom, you can do this either by draining the entire tank and cleaning it out, or you can keep the water in the tank and pump the sludge out of the bottom of the tank manually with a hose. Use a 50mm siphon hose and move it slowly across the bottom of the tank. You could also pump the sludge out with a motor operated pump. The sludge can be dug into the garden, as long as this does not violate your local shire regulations. You will lose a little of the water in the tank, along with the sludge, but it does mean you do not lose all of your water. And in many instances, you simply cannot afford to lose all your water, as there is no other water to use!

Regular maintenance checks:

Every three months

-inspect and clean gutters

-collection surface for debris and remove as needed.

-prune trees overhanging collection surface

-tank inlets for intact insect netting and leaf filters and replace as needed

-sides and roof of structure for integrity and any holes. Cover all holes as required

-inside tank for evidence of animal or insect activity, contamination or algae

-pipe work for integrity. Non self draining sections of pipe should be drained and cleaned

When you initially move onto a property with a rainwater tank as the household water supply, conduct a full inspection of the tank, collection surface and pipes. Check the integrity of all the structures and the cleanliness of the tank. Empty and clean the tank if you are doubtful about the water quality. Water quality testing is not usually required for domestic tanks, especially if all the regular maintenance has been carried out, and the tank is inspected regularly and cleaned as required. Until you are satisfied that the water in the tank is safe to drink, drink water from another source or use bottled water. The water will be fine to use for showering and clothes washing even if you believe it is not suitable to drink or use for cooking. If the water tank you inherit is old and in serious need of repair, it may be safer and less problematic to replace it with a new tank. The costs will need to be calculated, to determine if it is better to replace the tank or to use an alternative water source.

Calculating how much water you will collect:

Roughly speaking, not allowing for evaporation and absorption by surfaces, you can calculate the amount of water you will collect in your tank by multiplying the average rainfall (in mm) for your area by the size of your roof (in m2)