Many household products contain synthetic or natural chemicals in quantities that can cause pollution. Many chemicals occur naturally, but in small quantities that can be easily filtered or purified by groundwater and aquifer, or diluted into rivers and streams so they do not cause harm to the environment. However, when large amounts of chemicals are added to the groundwater table from landfills, dumping, or daily use, they can harm the biotic abilities of water so useful bacteria, fish, or plants cannot grow.
Most waste facilities now have guidelines for disposing of harmful chemicals used around the home, including ammonia, bleach, and heavy metals. When switching from normal household products to organic or natural products, care must be taken that the old products are not simply thrown in the trash, where they can leak into the groundwater and spread to rivers. Instead, chemical wastes should be consolidated into single containers and brought to waste facilities for recycling.
The containers themselves are also hazardous if discarded in large numbers. Many plastics are stable only in dry and neutral temperatures; when exposed to extremes of hot and cold or soaked in water -- or other chemicals in the same landfill -- plastics can break down into non-organic, non-soluble particles that can kill fish or discourage plant growth. Plastics should be brought separately to be recycled and cleaned if possible.
For other hazardous materials, it is always best to consult local waste management. Some facilities do not have the capabilities to recycle heavy metals or Compact Fluorescent Lightbulbs (which contain a small amount of mercury) and so those items must be transported to the proper facilities. Many Big Box stores (Home Depot, Lowe's) are able to receive and recycle CFLs, so check the local government waste management websites.
One important thing to remember is never to simply pour unwanted products down the drain; in cities, all liquid waste travels through a sewer system to a recycling facility, but the sewers are not completely airtight and so chemicals can leak out. All liquid waste in the ground will eventually join with groundwater and if there is too much of it, it will affect the water table's ability to naturally purify water. The groundwater and aquifer are one of the Earth's major water recycling systems, and without them plants and animals will be unable to access pure water.