Water reduction means there is a leak somewhere. It can be a radiator hose or even head gasket. You need to find a competent mechanic. Otherwise you will keep on pulling your hair for a while.
Secondly, if a/c is not functioning well then it also needs to be thoroughly inspected by a/c shop. It can be the compressor issue, low refrigerant/gas, leaking evaporator, clogged condenser etc. Only a professional can confirm.
