A drip irrigation system comprising in combination an inlet conduit to receive a supply of water to be distributed, a sand filter system adapted to be backwashed connected to the inlet conduit, a manifold receiving filtered water from the sand filter system, a plurality of distribution conduits connected to receive water from the manifolds, and at least one emitter connected to each distribution conduit for emitting water therefrom. Optional features of the invention include: a penetrable plug disposed in at least one of the distribution conduits, the plug being penetrable by a probe for measuring pressure in the respective distribution conduit and being self-sealing to close the puncture caused by the penetration after the plug is removed; the inclusion of at least two sand filters in the sand filter system whereby one can be backwashed while the other continues to supply water to the irrigation system so that irrigation does not cease during the backwashing; and the provision of retention screens downstream of the sand filters adjacent to which a sight-glass is provided for visual inspection of the condition of the upstream sand filter.
