Household rainwater storage and recovery systems

oszczędzanie wody

Water is one of the key natural resources that determines life in the universe, at least biological life that science has so far recognised. Recent NASA reports inform us of the discovery of massive salt lakes hidden beneath the surface of Martian ice caps – life may exist there too. But let’s return to Earth.

There is a problem with water, especially fresh water. It is beginning to become scarce, with additional disparities in access to clean drinking water, exacerbated by global climate change and access to sanitation solutions and technologies that enable the rational management of this precious resource. In Poland, we are also beginning to increasingly face periodic shortages of water and, perhaps paradoxically, a temporary surplus. And this is where another very key factor relating to rainwater management comes in. It is the degree of surface sealing. We like to have everything asphalted or covered with concrete, but isn’t this predilection fatal to us? It turns out that it often is. Large urban agglomerations are not able to cope with the demands placed on them by a rather unstable climatic future. Long-term droughts are increasingly linked to water shortages, bans on the use of mains water for irrigating green spaces. As well as creating impermeable barriers to water, concrete and asphalt also generate a heat island effect. This means that the air temperature in cities is often much higher than that in undeveloped areas, the air has lower humidity and a higher content of volatile pollutants and allergens. This is also compounded by increased evaporation of water from green spaces, which, if deprived of water, turn into dry deserts and the dying vegetation ceases to perform its ecosystem services (e.g. precipitation generator – pollen and fungal spores and bacteria living on the leaf blades of tall trees are nuclei of condensation and accelerate the formation of rain clouds). Less rainfall, water shortages, prolonged droughts, dying vegetation – all of this causes the soil in urban areas to lose its water storage capacity. Then come sudden, short-lived storms bringing heavy rainfall, the sodden soil does not take in excess rainwater, a massive surface run-off is created that the storm and combined sewer systems cannot accommodate. The consequence is flooding and consequently damage and costly repairs. We lose out on ecology, public health, local and global economics because of this. I got involved in the first major project related to the dissemination of so-called good practices in urban water management when I was still a teenager and high school student. That was 20 years ago and I still don’t see the desired systemic change. The large-scale changes we so desperately need. But let’s not fold our arms. Let us act at every possible level of the organisation of our social life. Let us therefore ask ourselves some questions. How can we rationally manage rainwater ourselves? What solutions and technologies are available that we can use? How do we implement them in our daily lives? And do they deliver the expected results and the anticipated savings?

Firstly: let us anticipate the future and design with it in mind.

Don’t get me wrong. It is not a matter of seeking help from a local soothsayer or fortune teller. It is enough to analyse for ourselves the past years in terms of rainfall distribution and look for a general trend that will shape the distribution of this rainfall over the next decade. This is enough to see that we are in for a very turbulent water management adventure. The demand for water is steadily increasing, the resources we can easily use are steadily diminishing. We are being hit by longer and longer periods of drought and more frequent interruptions of mains water supply. On the other hand, we are just as often confronted with violent, torrential rains. At this point I have two pieces of advice:

1.The problem is often a solution in itself;
2. Make hay while the sun shines.

Logic dictates that if I know I may have a water shortage problem (prolonged droughts), I should probably start collecting and storing water when there is an excess (heavy rains). This is what all kinds of rainwater storage techniques are for.

There are a huge number of solutions on the Polish market that we can use. I will already point out that a 200l barrel placed under a gutter is not enough. Let’s focus on solutions that will allow us to survive a prolonged drought. Is 200l of rainwater enough to water a home garden for 3-5 weeks of drought? Of course not, and so let’s abandon that romantic image of water dripping into a beautiful oak barrel. Let’s start counting. Quantifying our water consumption will allow us to calculate the size of storage that will be able to provide us with at least 50% of our water needs. With a reasonable amount of money at our disposal, we are able to build a domestic installation that will allow us to accumulate a water storage of 6-7 m3.

What do the regulations say?

The regulations and requirements defining the conditions for rainwater capture and collection are quite clear. Pursuant to the Regulation of the Minister of Infrastructure on the technical conditions to be met by buildings and their location, each household is obliged to discharge rainwater into the rainwater or combined sewer system and it is also possible to discharge such water onto its own land. In the latter case, under no circumstances is excess rainwater draining from the impermeable surfaces of our property allowed to enter neighbouring properties or streets. Drainage of rainwater onto green areas is of course very beneficial to the plot, but when we cover large areas around houses and other buildings with paved surfaces (asphalt, concrete), the soaking of the water into the soil becomes difficult and sometimes even impossible. Excess water also means a risk of damp foundations and even localised flooding.

How and for what purpose can we use rainwater?

Water for sanitation and water for drinking often come from the same source, the water supply system. The real needs in terms of quality of these two resources are significantly different, and the fact that we are constantly facing a shortage of drinking water should give us food for thought and prompt us to take specific measures. At the level of individual households, solutions can be implemented to improve this situation. Diversifying the source from which we obtain water for the household can result in real savings on water and wastewater charges, contributes to saving valuable treated water resources for drinking and helps to manage rainwater.

External and internal use of rainwater

The obvious use of captured rainwater is to water plants in the garden. In the event of prolonged hot weather, gardening enthusiasts can spare no effort to keep their manicured gardens in impeccable condition by using considerable amounts of water for irrigation purposes, including that from the water supply. Less obvious water uses include washing cars, cleaning paved surfaces with pressurised water, filling garden ponds, ponds and pools, or powering fog curtains during hot weather. I think this list can be extended to include more creative ideas. Rainwater can also be used inside households for flushing toilets or doing the laundry. But we also have solutions for treating rainwater to drinking water quality. Both categories of rainwater use will have an impact on the size and construction of rainwater harvesting and treatment facilities.

Under or above ground?

This is a common question that builders ask themselves when considering where to place tanks for storing large amounts of rainwater. Both solutions have their advantages and disadvantages. If we opt for the more popular solution – burying the tanks underground – we gain in visual aspect, but we lose in terms of the economy of such a solution, as it imposes in advance the necessity of using pumps that consume electricity and generate operating costs. In addition, locating the tanks underground will make any maintenance work more difficult and, in the event of a tank failure (e.g. rupture, puncture), expose us to even higher costs. Less popular for aesthetic reasons, the solution of locating the tank above ground opens up a number of interesting possibilities. Firstly, the gravitational distribution of water in the garden. A tank positioned to capture water from the roofs of buildings, but located at ground level or even a few tens of centimetres above it, allows it to be easily cleaned in the event of sediment build-up and to use gravity to bring water to any point on the ground below the tank outlet. This often allows the pump to be dispensed with altogether. Keep in mind that if the tank is located above ground, it can always be neatly integrated into the surroundings with climbing plants.

Prevention first

It is also worth taking into account any possibility of pre-treating the rainwater stream from as many impurities as possible (leaves, sand, dust or other organic matter). Gravity basket filters, suitably protected gutters, first flush diverters, ozonators, etc. will help here. With air pollution on the rise, let’s not be under any illusion… Rainwater is not pollution-free water. In addition, the degree of pollution also depends on the type of roofing and its condition (peeling paint from sheet metal roofing can also be a source of toxins entering the water). Leaves falling on roofs and droppings of birds or other animals (cats, martens, etc.) cannot be overlooked either. It is better to catch these pollutants in front of the tank than to remove them from the water in it.

Drinking rainwater

The biggest challenge is the treatment of rainwater for drinking purposes. Interesting solutions from the DIY area are suggested by users of self-sufficient houses, often built from waste, or so-called Earthships. The principle of these buildings is to be completely self-sufficient, so interesting solutions have been introduced for supplying residents with water. Similar systems can be installed on their own in more traditional buildings. There are also many solutions waiting on ‘shop shelves’. My personal observation on many popular solutions is this: most commercially available systems work with pumps, replaceable filters, high-pressure filtration membranes and disinfection systems based on UV lamps. All these solutions are dependent on electricity supply. When thinking about possible upcoming crises, it is also worth considering solutions that can work in situations of power failure in the grid (e.g. emergency power supply from a generator, obtaining energy from photovoltaics or other RES solutions, using gravity filtration solutions or hand pumps).

Does rainwater storage and reuse pay off?

In practice, the benefits of rainwater harvesting go well beyond the financial benefits. Rainwater is soft water and therefore does not have a detrimental effect on the life of the water system in the house and the many appliances that can be fed with such water (washing machine, dishwasher, etc.). Deciding only to supply the tank for flushing the toilet with rainwater can save the most, because, according to various sources, between 25 and 30% of water is used for this purpose in households (for cooking only 3-5%). Add to this the consumption for cleaning, and we gain another 30% of water saved. We can also combine the reuse of rainwater with grey water recovery systems to save even more. It is important to consider all these solutions when designing elements of our immediate environment (buildings, paved areas, green spaces – e.g. rain gardens).

Finally, returning to the broader context of rainwater management in cities, the very design of paved surfaces so that they are several centimetres higher than the surrounding green areas (lawns, greens, etc.) will allow large amounts of rainwater to be stored in the landscape. Winter is ahead of us, i.e. the period of fighting ice and snow accumulation and, consequently, managing meltwater – in this case, too, it is worth implementing ecological solutions, e.g. abandoning the use of NaCl (sodium chloride) for salting streets in favour of the less harmful MgCl2 (magnesium chloride).

Building a sample rainwater storage system

A clean roof and gutters means clean rainwater. If you are thinking of building your own rainwater storage system, start by tidying up your roof situation. In case tree leaves fall on your roof and get into the gutters, it is a good idea to secure them with suitable protective nets. Another solution is to fit a leaf separator to the vertical gutter downpipe. This is a component that will rid the water of larger particulates before they enter the tank. The tank itself will probably be the most costly part of the whole system. You have to reckon with a cost of around £5,000 for a 4-5 m3 tank. If you plan to use rainwater also in winter (e.g. for washing or flushing the toilet), it is worth investing in an underground tank or a well-insulated above-ground tank (with insulation to prevent water from freezing during severe frosts). Another way, which I admit is rare, is to connect a small solar collector (vacuum tube collectors are best here) to heat the water stored in the above-ground tank. An additional filter basket can be installed at the entrance to the tank to catch the remaining solids from the water stream. The water supply pipe to the tank should enter the tank, extend all the way to the bottom, and be terminated at the bottom by a tee with two pipes turned slightly upwards. This part of the installation is shaped like an anchor. This arrangement will allow the energy of the water to be dissipated, so that sediment that collects at the bottom of the tank will not be picked up and mixed with the stored, clean water. The water discharge pipe from the tank should also have an elbow pointing upwards, and the water intake should start in the middle of the tank so that sediment is not sucked up from the bottom. The tank should be fitted with an overflow pipe to allow for safe drainage of excess water so that the tank site is not washed away in the event of heavy rainfall and overflowing installations. Let me return to the issue of the sludge that will collect at the bottom of the tank and the biofilm that covers the inner walls of the installation after a while. This biofilm and sludge is formed by micro-organisms that grow in areas of long stagnant water. Recent studies in microbiology report that the micro-organisms living in such environments are very effective at absorbing and hyper-accumulating heavy metals and other toxins present in rainwater. Thus, the presence of sediment and biofilm is highly desirable and the holding time of the water in the tank should be a minimum of three weeks.

Finally, one more important feature of a good rainwater harvesting system. A very important feature is the inspection sumps and manholes that allow access to the tank, so that the efficiency of the system can be periodically checked, the excess sediment cleaned out and the tank kept in good sanitary and technical condition. Depending on the purpose for which the stored rainwater will be used, such a basic installation will be enriched with appropriate pumps, water treatment systems, ozonators or UV lamps, if we want to use such water for drinking.

Author: Łukasz Nowacki

The text was written as part of the project “Hydrozagadka – how to win against drought?”.