Why is foundation waterproofing necessary?
Foundations are basically holes in the ground that want to fill with water. Poor site drainage, through-wall penetrations, concrete cracking/mortar joints and movement, door/window/vent openings, flooding, high water tables, hydrostatic pressure – all contribute to the propensity for water to fill the subterranean void we have established. Foundation leaks are difficult and costly to rectify, not to mention designer/contractor financial liability. Water in a basement is water in a building. Excess moisture within a building is a recipe for higher RH and increases the potential for condensation, and mold and other allergens.
Luckily, foundation water intrusion is usually preventable. The goal is to identify all the potential water transport mechanisms, and address them, through good design practices, proper detailing, and quality execution.
Waterproofing is the process of making an object or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environments or underwater to specified depths.
Water resistant and waterproof often refer to penetration of water in its liquid state and possibly under pressure, whereas damp proof refers to resistance to humidity or dampness. Permeation of water vapour through a material or structure is reported as a moisture vapor transmission rate (MVTR).
The hulls of boats and ships were once waterproofed by applying tar or pitch. Modern items may be waterproofed by applying water-repellent coatings or by sealing seams with gaskets or o-rings.
Waterproofing is used in reference to building structures (such as basements, decks, or wet areas), watercraft, canvas, clothing (raincoats or waders), electronic devices and paper packaging (such as cartons for liquids).
How local code requirements and flood zone classification could affect you
Before we get to the solutions, you need to understand how water tables, flood zone restrictions, and code requirements could impact you. 
If local code requires compliance with International Building Code (IBC), waterproofing is required where a hydrostatic pressure condition exists and dampproofing is required where it doesn’t. If the foundation lies below the local water table, a hydrostatic condition is present and waterproofing is required. Appendix G additionally defines requirements for flood resistant construction in regulated flood zones. You can determine if your building is in a regulated flood zone (high risk, AE & VE zones) by looking at the FEMA flood zone maps or Flood Insurance Rate Map (FIRM).
Understanding the three foundation waterproofing system types and when they are used
There are three basic types of waterproofing systems: blind-side and positive-side (new construction), and negative-side (new or existing construction). All types rely on the waterproofing membrane to be continuous and water-tight.