Acid rain.

Acid rain is acidic rain. It occurs when sulphur dioxide and nitrogen oxides enter the rain, making it acidic. It is very harmful to the water cycle because of its harmful effects on animals and dissolves the nutrition that plants and trees need. It causes very big health problems for animals or even death. This mainly happens when it enters oceans etc. You can prevent it by not littering.

Pollution

Pollution is when a harmful object or substance enters the environment. pollution is very harmful to the water cycle because it can lead to acid rain and effects climate change significantly. It also reduces the amount of solar radiation that enters the atmosphere. You can prevent pollution by NOT littering, reducing the amount of solar radiation entering our planet Etc.

Greywater recycling

Greywater is water that is reusable under the right circumstances. You get it from your household water supplies. Basically whatever you use water for. Greywater is either treated or untreated, which depends on what you can use it for.

Solar power

Efficiency:

Solar power is very efficient, as it converts about 15-22%  of the energy into usable energy but it depends on things like placement, orientation, weather conditions etc.

Cost:

Solar power is quite expensive, but it depends on what solar power you are using. If you are using solar panels then they usually cost between $3,000 and $12,000.

Wind power:

Efficiency: Wind power is purposely below halfway efficient because if it was high when the wind goes into the turbine, the wind would just drop. Wind power is about 30-45% efficient increasing to 50% during peak wind times.

Cost:

It is a lot cheaper than solar power. It costs about 40 dollars per megawatt-hour.

Coal power:

Efficiency: Coal power is about 33% efficient but very bad for the environment.

Cost: Coal is pretty cheap, it costs about $120 a megawatt-hour.