Q3. Restrictions should be introduced now so people get used to them. The extent of them can then be increased as and when needed. (for example a hosepipe ban one day a week now becoming  2, 3 4 ... or 7 days a week when needed)
Q4. No - this will cause hardship for some whilst other people will "hoard" water which will be wasteful. Reduced water pressure and bans/restrictions on dishwashers, washing machines etc would be better. Also encouraging people to fit showers and reduce/eliminate baths is more effective.
Q8. Progressively higher targets each year would be better. Also "penalty charges" on householders who dont maintain their pipes etc resulting in high water consumption due to wastage.