Builder damaging our property

A builder bought 12 lots on the street above our house (our house backs up to this area which is higher than our house in elevation). His drainage system is insufficient and he has flooded our property every time it rains for over 2 years. We hired a hydrologist who determined that their is water running under our foundation and that our house has a 99% chance of sustaining structural damage. The builder denies it is his fault (even though we have pictures of the water running off his property). We are sick of dealing with it and want him to buy our house so we can move out. We have been told we might lose in court because their is no physical evidence of the damage under our house. Can you force someone to pay for damage that cannot be seen or the potential damage that will be caused over time?