It depends where you live, but yes, the towers are enough in most flat lands. There are also usually pumping stations at critical points that treat the water. My small town where I grew up has a tower and a pumping station where the water quality is monitored. (My brother in law in in charge of it, so I was lucky to get some insight into it. He uses a spectrometer to make sure radon limits aren’t exceeded.) If you want to learn more about it, perhaps you could organise a visit to your local water works facility.
http://10mosttoday.com/10-coolest-water-towers/
Water pressure is usually regulated as water comes into the home by a regulator. It looks like this: http://www.hooverelectric.com/wp-content/uploads/2013/03/Detroit-Plumber.jpg
Because the water runs through a system of ever decreasing pipes, this actually accumulates a great deal of pressure on its own and the PSI has to be brought down by a regulator to save on strain in the pipes.
In some homes, especially those on hills (like where I lived in New Zealand) our hot water tanks and other holding tanks would be installed in our roofs to assist in increasing water pressure. This is also why tall buildings have water tanks on their roof because municipal water psi would become useless in the top stories, so they have to have their own system to build pressure in their internal pipes.
I hope this helps explain some of your question. Liquid dynamics is really more exciting than people think and we take it all for granted when we turn on our tap.
Here is a good ‘How Stuff Works’ http://www.howstuffworks.com/water.htm