How to use rainwater and grey water this summer

Kya deLongchamps shows how using rainwater and grey water reduces consumption of our precious resource

Rainwater is a huge benefit in summer when hosepipe bans can limit our use of fresh water around the garden. File pictures

Every day, each of us uses in the area of 113 litres of fresh water, and every day we lose around 37% of our treated water supply straight into the ground before it ever reaches a tap (Uisce Eireann). We may have won the battle against water charges (for now), but let’s show our respect for our most precious resource.

Together with reducing your freshwater usage wherever possible (water saving showers/energy efficient appliances/not running taps needlessly and so on) there are plenty of simple ways to manually divert your processed, grey supply, and to harvest rainwater in volumes easily turned over for use around the garden.

Grey water is not especially dirty despite its grizzly moniker, but as largely biodegradable rinse water, it’s not entirely clean and it’s not “potable” (suited to drinking). You can collect buckets and jugs of grey water from humdrum domestic activities including bathing, using your condenser tumble dryer, washing the dishes and the water collected in your humidifier. Even when we’re not under a hosepipe ban in the sweatiest days of summer, its Earth-friendly thinking.

Sophisticated grey water systems that collect water from the bath, shower and laundry, pumping it off to fill the toilet cisterns, for instance, are not cost-optimal for most families and not widely celebrated by the environmental lobby. Stored grey water must be disinfected for starters. 

The environmental charity the Centre of Alternative Technology (UK) points out, “ It’s important to look carefully at the design and operation of any system for reusing rainwater and grey water. A complicated system may not be an effective way to reduce your environmental impact.” 

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It suggests a watering can and bucket bought for a tenner outweighs the expense and hassle of grey water engineering that costs thousands.

Grey water is not comparable to rainwater. Pressed into use for washing, it inevitably has some physical and dissolved debris in it, and it more than likely has some bacteria and biodegradable material in there too. This is not water we want to store for any length of time. If you have a septic tank, that’s where it goes with your unspeakable “black water”. 

Kept more than a day, Nature will have her merry way, and grey water will grow slimy and smell unless filtered and purified using chemicals and UV light.

The cleanest grey water is condensed water taken from your tumble dryer. If it’s clear coloured, and you can’t see any floating lint on visual examination, that’s usually clean enough to pop into the iron. 

Water from the dehumidifier will reflect the quality of the air it was collected from, so not necessarily pure if your house has mould and damp issues or anyone smokes indoors. It’s also acidic in nature. To be on the safe side, blend it with tap water before pouring it over the spider-plant. 

Think about scale when choosing your rainwater harvesting vessel. A vertical thrust makes good use of a small footprint. 

Yes, I know there are highly committed green goddesses who have removed the U-bend from the wash-hand basin and are collecting grey water in a bucket directly for use in the loo cistern. I’m a concerned, planetary enthusiast, but I am not that warrior.

The first place to think of using your grey water is for healthy houseplants or out in the garden — especially in summer. 

We’re thinking here of hardy plants and trees that won’t be bothered by a little soap residue. Washing-up liquid is biodegradable, and as long as the water is carrying just a few food scraps, you can safety take this out for use in the garden once cooled. 

I find washing-up basins with raised handles much easier for this slightly comic job. To ensure the liquid is as safe as possible, choose brands like Ecover, Bio-D and Method, which are low in sulphates, dyes and harsh chemicals, and free of palm oil.

Ideally, in the cooler hours of early morning or early evening (when it won’t abruptly evaporate), slop the grey dish or condensed water around the base of the plant in a close circle, letting it seep down rather than hitting leaves and stems which might then be burned by the sun. No harsh deluge straight over the plant, not even from a watering can. We’re aiming to water the ground, allowing the plant to collect the water via its root system.

If you grow fruit and vegetables to consume, opinion is divided regarding leafy veg and root crops. 

Many horticulturists feel the plant is contaminated by grey water, and it’s true that some basin loads will contain a hefty amount of grease and slight chemical traces. 

Again, avoid splashes of the grey water directly onto vegetables and fruits, and wash them thoroughly before consuming them (good advice in all cases). 

Keep in mind, if it’s from the bath — well, not to be crude, but there may be a few curly hairs backstroking through the bucket. Grey water is not recommended used neat on seeds, tender seedlings and some houseplant varieties. Look up the species before gifting them the grey stuff.

Diverting grey water through valves, pipes and straight out to a dedicated irrigation system is possible, but most gardeners reroute stored rainwater. Free of dishwasher salts, detergents and other pollutants, rainwater is purer, the pipework is simpler to arrange, and let’s face it, we’re in Ireland. 

Plants and trees are designed by the universe for rainwater, not treated tap water, so use it wherever you have the choice to avoid a subtle build up of pathogens on the soil.

Every house with a sloping roof has a rainwater collector right there, ready to go. Inventive allotment owners and smallholders suspend tarps to act as onsite collectors. 

Genius. 

Using a diverter valve and a barrel you can take water off the house, outbuildings, sheds, wherever there’s a gutter, downpipe and a place for a rain barrel. Raising the butt off the ground, allows us to not only fill watering cans easily, but to put some gravity helped pressure into the spout and hose. You can use bricks or blocks, or an optional stand, but ensure the kit is stable as a full barrel is extremely heavy.

Immersed in the barrel, a mains-fed or well-fed store and pump can push water to both drip-style irrigation lines and lengths of hose at distant parts of the garden. Lidl offers a 400w model for just €29.99. Otherwise expect to pay in the area of €60-€220 for a quality brand that can handle debris up to one millimetre in diameter. 

Ensure you match the flow rate (litre/hour) and the submersion level to your needs and the dimensions of the barrel. Tanks can be buried in the ground, holding large amounts of rainwater for pumping back out for household use, or around the beds of a smallholding.

Pumped or bucketed, clean, filtered rainwater is also suitable for the first soapy attack when washing cars, but used here or on the windows, it’s vital to ensure there is no sharp dirt in rainwater coursing off a dirty roof. Because rainwater is soft, it won’t disrupt sealants and waxes on the paint, but is not suited to a final rinse, which could result in water spots and light staining. 

Again, the quality of the water will depend on your situation, and you can expect rainwater from a city roof to carry some petrochemical residues. According to a study from Stockholm University, published in 2010 and authored by Professor Ian Cousins, rainwater is unsafe to drink all over the world. Don’t use it to top up even your pets’ supply.

Sizewise, if you have a standard sized garden and a few containers, a 200l rain-barrel is about right. Ensure it has a secure lid to avoid children, pets or wildlife getting curious. 

Profiles of barrel can be found for just about any space, and in a UV-stable recycled plastic they should last a decade or more without difficulty. With a flexible connector, the guttering and downpipes don’t have be bang up against the barrel. 

You can also connect two barrels together to keep a low profile (buy the same brand to avoid complications when you drill out the connection points). The chief collection period for rainwater is just about over, so if you’re considering a new, beautiful butt, get one sooner rather than later.