The world’s cities are in constant flux, being built or built upon to accommodate fast-growing urban populations. The standard approach to urban design has changed, as it has countless times throughout the ages. Today, a new trend has dawned: sustainable design for greener cities, and ultimately a greener planet.

Sustainable design boils down to two main goals: conserving energy and reducing waste. There are many innovations that deliver these goals that are worth paying attention to. After all, they could be staples in the future of urban design, construction, and renovation. As a seasoned real estate entrepreneur, I find it useful to watch these developments carefully.

Here are seven innovations that, though not necessarily new, I believe may explode in popularity as cities are designed and developed with sustainability in mind.

1.Green roofs

Not unlike the habitats of the Hobbit’s Shire, green roofs are structures either partially or fully covered by vegetation. Why? The benefits are extraordinary. Green roofs limit the need for heating and cooling, filter pollutants from the air, insulate buildings, and offer extra square footage for agriculture. They also help mitigate the “heat island” effect in urban spaces — when cities are hotter than the surrounding land — by lowering temperatures.

The modern trend started in Germany in the 1960s and spread to other European cities, many of which are known for their sustainable initiatives. It’s an effective use of space that reduces energy consumption and adds new functionality to formerly barren roofs. North America also has a growing market for green roofs and other types of eco-friendly “living architecture.”

2. High-speed transport

Elon Musk’s future-forward Hyperloop has been in talks for years, and recently the much-hyped high-speed rail had its first public test. It could take many years to be fully realized, but it’s not the first of its kind: also known as bullet trains, high-speed railways can be found in Japan, China, France, Germany, Russia, South Korea, the US, among other countries.

Though expensive to build, high-speed rails are generally eco-friendly and save in greenhouse emissions by providing a speedy alternative to more fuel-intensive transport. Just look to California, where high speed rails run on electricity and reduce the need for cars. In future cities, mitigating the need for vehicular and air travel by implementing high speed rails instead will save dramatically on energy usage and mitigate pollution, too.

3. Floating buildings

With so much land overtaken by human activity, expanding onto the water could preserve greenery for agriculture and other uses. There are various of types of floating architecture designed precisely to be eco-friendly urban solutions.

Self-sustaining floating house units already exist: for example, the WaterNest 100 by EcoFloLife is made of 98 percent recyclable materials, with photovoltaic panels embedded in the rooftop for solar energy. This type of innovation could work for an entire city, in theory. In fact, various eco-friendly floating cities have been designed, including Belgian architect Vincent Callebaut’s Lilypad, proposed as a city for climate refugees, and Silt Lake City, which would float atop the Nile River.

4. Water recycling

Speaking of water, droughts and shortages are predicted to become increasingly common as populations grow, supplies dwindle and the planet warms. Americans in particular use 100 gallons per day, 95 percent of which is wasted. Certainly there is a more efficient way to conserve water, in and out of cities.

Greywater refers to water in sinks, showers, washing machines, etc: essentially all streams but toilets. Greywater, along with stormwater and even wastewater can be better managed and recycled for reuse in urban settings through large-scale systems and smaller-scale innovations like this high-tech shower that recycles water as you wash.

5. Solar solutions

Solar is one of the fastest growing forms of sustainable energy and one of the most promising too. But for all the hype, it faces some key problems: mainly, the fact that sunlight isn’t always a guarantee.

Even so, solar technology is becoming better and more efficient, and more easily stored for not-so-sunny hours. One Swedish company is able to power 24 homes with one dish, and Tesla now offers a solar battery at the most affordable price yet. Individual solutions like these could be scaled up for implementation in urban areas, like this solar road used in the Netherlands that generates enough power for a year’s worth of electricity.

6. Microgrids

Solar energy is great for easing reliance on the electrical grid, but grids will likely be necessary in powering cities for a long time. However, there are less wasteful ways to provide electricity, like the use of microgrids for example.

Microgrids are small, decentralized energy systems that collect, store and distribute electricity in an even and balanced way. Where large-scale power plants are often powered by fossil fuels, localized grids are better suited to sustainable energy sources like solar and wind, and can act as backup in case of blackouts. For cities, a network of microgrids would waste less energy and derive it from a variety renewable sources. The market for microgrids is expected to grow to $40 billion by 2020.

These are just several of the innovations that are likely to inform sustainable design in cities as we move into a more environmentally-conscious future. Whether all at once or a little at a time, the urban greening trend shows no sign of sunsetting anytime soon — which is why it’s smart for those in the real estate industry to take note and adapt.