Understanding a few basics about plumbing and drainage systems can go a long way in figuring out plumbing problems and explaining them to the plumber that you hire. 

fresh water flowing out of a tap
Fresh water flows out of your taps
Image - Spraytan.net
Did you know that the plumbing system in your home actually consists of two parallel systems? One system brings in the clean, fresh, treated water to your taps and machines while a completely separate system carries used, dirty, waste water out. These systems need to work in tandem to prevent plumbing problems. It is important to hire a professional plumber/ plumbing service with the right credentials and experience to install the plumbing system in your home correctly. 
Here we discuss basic information about the fresh water plumbing subsystem. 

Fresh Water Plumbing Subsystem

the main water valve
The main water valve
Image - Prorestoration.com
Fresh water is usually pumped into your home past a water meter that records your water usage and then you receive a water utility bill at the end of the month. Somewhere close to your water meter will be a water mains valve that will control the flow of all water to your home. In case of a leak of a burst pipe it is important to know where the water mains are to prevent damage to your home. Water fixtures like taps and machines like water geysers, dishwashers and washing machines in residences usually also come with individual cut off valves. Individual bathrooms and wet areas usually have a main valve as well that can be used to shut off water to a part of the house without inconveniencing the whole family.
fresh water subsystem carries clean water
IThe fresh water subsystem carries clean, potable water to your taps
mage - Rockwellautomation.com
The fresh water subsystem is where you will need t install filtration or water softening systems to protect the pipes as well as your appliances. It is also a good idea to check the quality of water in your area, hard or soft? And decide to install a water softener while the plumbing system is being planned instead of later on.
ripple caused by a drop of water
Image - Wwf.org.uk
The fresh water system in most Indian homes involves pumping clean, potable water up to a water tank placed at a height above the house. Water storage facilities, like a tank, placed at a height help water to travel to your taps with some pressure due to gravity. So if you have low water pressure in a tap suddenly one of the reasons could be no water in the tank, or silt blocking the pipes, preventing the water to reach you at a pressure. Hire a water tank cleaning professional on Hometriangle in this case and not a plumber! A basic explanation of your drainage system follows soon!