Ask This Old House season 4 episode 3
Episode title: Under-Sink Water Filter; Planting a Drought Resistant Tree
Plumbing and heating expert Richard Trethewey helps a homeowner improve the quality of her drinking water by installing an under-sink filter. After that, Richard and host Kevin O'Connor are joined in the loft by water-filtration expert Bill McTighe who explains several other types of residential water filters. Then, landscaping contractor Roger Cook helps a homeowner select a drought-resistant tree and plant it properly in her sloped front yard.
