The water concept of our guest house – building block of sustainable tourism in Cape Town

Our vision of a sustainable guest house

When we were planning the house, it was clear to us from the outset that we also wanted to be sustainable and independent in terms of water supply. Firstly, it was important to us to use the valuable resource of water carefully without anyone having to sacrifice comfort. In our view, there is no contradiction between luxury and sustainability, but they hand in hand. This is how we envision a contemporary concept of sustainable tourism in Cape Town.

Grey water treatment drastically reduces water consumption

So, we started to look into grey water treatment. The basic idea is simple: you collect the water that is used for showering and washing, for example, purify it and reuse it, e.g. for flushing toilets and watering the garden. This saves between 30% and 50% of water.

In order to recycle grey water, two completely separate pipe systems must be provided in the house for the inflow and outflow. This separates fresh water, grey water, other waste water and treated grey water. We decided to use only the grey water from showers and washbasins, because this is where the treatment works particularly well. Of course, this requires a tried and tested filter system. After intensive research, we found the latter at Intewa in Aachen ( who fortunately also work together with a specialised installer in Cape Town (

Rain water makes us fully sustainable and independent

We didn’t just want to reduce water consumption, we wanted to be completely sustainable and independent. That only works if you utilise the rain. At 500-600 litres per sqm per year, Cape Town actually gets enough rain, but it’s concentrated in the winter months from May to September. This is good for all guests, who can enjoy the pleasant climate in the other months, but poses a particular challenge when it comes to utilising the rainwater: it has to be collected and stored in winter so that it is available in the dry summer months. Many people solve this problem by drilling a borehole and using natural reservoirs. However, this does not work everywhere, as we had to learn the hard way.

After a first setback we found the right solution

Our original idea was to use some large tanks in the plant room as water storage and also to drill a borehole. But things turned out differently: after hiring a dowser, various supposedly scientifically sound measurements and two very costly but unfortunately futile drillings to a depth of 173 metres, i.e. about 30 m below sea level, we gave up in extreme frustration.

Now we had to come up with a new plan. Without a borehole, the only alternative was a storage tank large enough to supply the whole house during the summer months. We then examined various options with Jeanette and our structural engineer and finally decided in favour of an underground water reservoir – a cistern. A huge hole was excavated in front of the existing house – where the driveway is today – and a kind of underground pool with a concrete ceiling was built with a capacity of 120,000 litres.

Together with the tanks on the ground floor, we now have around 150,000 litres of storage capacity – more than enough for an entire season. With our roof area of around 500 sqm, which we use to collect rainwater, we could theoretically fill the tank twice a year. So even if less rain falls in one season, it’s enough.

But rainwater is not yet drinking water. So here too we needed a good, tried and tested filter system, which we again found at Intewa. They are the technical leader in both areas – rainwater utilisation and grey water treatment. Of course, we looked at alternative suppliers. But Intewa clearly came out on top.

It is not easy, but with the right partners it works

Our building contractor was also critical at first. The installation and technology, in which four different trades have to work closely together, are quite complex: water installation (double pipe system), hot water generation (heat pump and storage tank), water treatment (rainwater and grey water) and horticulture (irrigation system).

We therefore appointed a specialised water engineer in addition to the four companies in order to be able to solve all the interfaces and challenges that arose. In the beginning, everything that could go wrong did go wrong and we were so pleased that David, our water engineer, worked calmly and competently with everyone involved to solve all the problems and coordination issues. When you turn on the tap or get in the shower, you don’t think about everything that has to work together to ensure that water flows. But the good news is: if you get it right and have the right people, it works.