Domakihub Install a Rainwater Harvesting System and Cut Water Bills
A practical guide to collecting, storing, and using rainwater at your home, rental, or hotel in Greece.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
Greece's long dry summers and rising water costs make rainwater harvesting one of the smartest investments you can make in a home, holiday rental, or small hotel. The video above shows a landscape contractor walking through a complete residential installation, so you can see exactly how the components connect before you buy a single fitting. This guide breaks the project into clear steps, explains where a licensed plumber must be involved, and helps you prepare so the job goes smoothly and stays code-compliant.
Why Rainwater Harvesting Makes Sense in Greece
Greece receives the bulk of its rainfall between October and March, with some regions logging 600–900 mm per year. A modest 100 m² roof surface can capture 60,000–80,000 litres in a single season — enough to cover garden irrigation, toilet flushing, and outdoor cleaning for much of the year without touching the mains supply.
Holiday rentals and hotels benefit even more: high occupancy in summer coincides with peak water prices and occasional municipal restrictions. A well-sized tank smooths that gap and signals environmental responsibility to guests, which is increasingly a booking factor.
Understanding What the System Involves
A rainwater harvesting system has four main parts: the collection surface (usually the roof), a first-flush diverter that discards the first dirty runoff, one or more storage tanks (above-ground or buried), and a distribution circuit that sends stored water to non-potable end uses — irrigation, toilets, washing machines (if filtered), or external taps.
Connection to indoor plumbing for toilet or appliance supply requires a licensed plumber in Greece. The reason is cross-connection risk: mains water and harvested water must be kept completely separate, with air gaps or backflow preventers mandated under the building code. A plumber will also ensure any underground tank installation meets local authority requirements and that the system is correctly labelled so no one accidentally drinks harvested water.
How to Install a Rainwater Harvesting System: 5 Steps
- 1
Size your system and choose a tank
Start by measuring your roof catchment area in square metres and looking up your local annual rainfall (the Greek Meteorological Service publishes municipality-level data). Multiply area × rainfall × 0.85 (runoff coefficient for tiles) to get your annual yield in litres. Choose a tank that holds roughly 20–30 days of your target consumption — for a three-bedroom home supplying toilets and irrigation, 5,000–10,000 litres is a common starting point. Polyethylene tanks are the most cost-effective; concrete or fibreglass suits large buried installations. Confirm tank dimensions against the access route to your site before ordering.
- 2
Install or adapt the gutters and downpipes
Every downpipe feeding the system needs a leaf guard at the gutter outlet and a first-flush diverter fitted low on the downpipe. A first-flush diverter holds back the first 20–30 litres of each rain event — the dirtiest water — in a standpipe that slowly drains between showers. This one component dramatically reduces the sediment, bird droppings, and roof dust that would otherwise reach your tank. Use UV-stabilised fittings outdoors; standard PVC degrades in the Greek sun within a few years.
- 3
Position and prepare the tank
Above-ground tanks must sit on a flat, compacted base — a concrete slab or compacted gravel pad rated for the full weight of water (1 kg per litre). Keep the tank shaded or choose an opaque tank to inhibit algae growth. For buried tanks, excavation depth must account for the tank's inlet height relative to the lowest downpipe; this almost always requires a plumber or civil contractor to plan the fall and confirm that no existing drainage or utilities run through the dig zone. Leave a 300 mm service clearance around the tank on all sides.
- 4
Connect inlet, overflow, and a calmed inlet pipe
Run the downpipe output into the tank via a calmed inlet — a pipe that extends to near the tank floor and bends horizontally, releasing water gently to avoid disturbing sediment. Fit a stainless-steel or nylon mesh filter (200–500 micron) at the tank inlet. The overflow pipe must be at least as large as the inlet pipe and must drain away from the building foundation to a soakaway, drain, or garden — never back toward the structure. Fit a mosquito-proof mesh over every opening; stagnant water in Greece can become a breeding site within days in warm weather.
- 5
Set up the pump, filtration, and distribution — with a plumber for indoor use
For garden irrigation only, a simple submersible pump and garden hose connection is within a capable DIY installer's reach. For any indoor supply (toilets, washing machine), engage a licensed plumber. They will install a pressure pump, a sediment pre-filter, a UV steriliser or fine carbon filter, correctly labelled non-potable pipework (Greek standard: violet pipe or 'ΜΗΠΟΣΙΜΟ' labels), and a backflow preventer on any point near the mains. The plumber will also register the installation if required by your municipality and carry the liability if a cross-connection is ever alleged.
Rather have a pro handle it?
Get a vetted plumbing pro in your city — one number, booked in EN/EL/DE.
FAQ
- Is rainwater harvesting legal in Greece?
- Yes, collecting and using rainwater for non-potable purposes (irrigation, toilet flushing, cleaning) is legal throughout Greece and is encouraged by national water policy. There is no permit required for a simple above-ground tank feeding garden irrigation. Buried tanks and any indoor connection to building plumbing should be declared to the local authority or building service (Πολεοδομία) and must be installed by a licensed plumber to comply with the building code.
- How long does a typical installation take?
- A straightforward above-ground system — gutters cleaned, first-flush diverter fitted, tank placed and connected to the downpipe — can be completed in one to two days by a competent tradesperson or experienced DIYer. A buried tank with an indoor non-potable circuit typically takes three to five days including excavation, backfill, and plumbing, and should be quoted as a single job with a plumber.
- How do I keep the stored water clean between rain events?
- Three practices cover most of the risk: keep all tank openings mosquito-meshed and light-proof; clean the first-flush diverter standpipe and the inlet filter at the start of each rain season; and if water sits unused for more than four to six weeks (common in summer if you switch to mains), dose the tank with food-grade chlorine at 2–5 mg/litre and run it through before resuming use. An annual tank inspection — looking for sediment build-up, biofilm on walls, and integrity of seals — takes under an hour and prevents larger problems.