1. The sanitary engineer is concerned with hydrology. - Present Simple Passive
to concern
2. Different systems of water filters are used in present day. - Present Simple Passive
to use
3. Water finds its way to the rivers. - Present Simple Active
to find
4. Ocean water contains salt and other mineral materials. - Present Simple Active
to contain
5. The earliest written records of water purification date to 2 000 B. C. - Present Simple Active
to date
6. The modern recreation center has been erected in the center of Moscow. - Present Perfect Passive
to erect
